logical.java

/*
** Module   : logical.java
** Abstract : Progress 4GL compatible logical object
**
** Copyright (c) 2005-2024, Golden Code Development Corporation.
**
** -#- -I- --Date-- --JPRM-- ----------------------------------Description----------------------------------
** 001 GES 20050517   @21233 Created initial version with full support
**                           for all Progress logical processing including
**                           all operators (AND, OR and NOT are in this
**                           class and all others in the parent class) 
**                           and the unknown value.
** 002 GES 20050607   @21444 Minor additions for function support.
** 003 GES 20050621   @21534 Added an assign() method to modify this
**                           instance's state based on the result of
**                           an expression of compatible type.
** 004 GES 20050721   @21765 Added a constructor that takes a string and
**                           merged cloning for SVG.
** 005 GES 20050815   @22120 Added Undoable interface support.
** 006 GES 20050830   @22385 Added error condition processing.
** 007 ECF 20051004   @22971 Implement hashCode() method. Required to be
**                           consistent with BaseDataType's implementation
**                           of equals() method.
** 008 GES 20051022   @23088 Handle the case of an OR operator with both
**                           operands as unknown.
** 009 GES 20060206   @24302 Made compareTo() safe to process any object
**                           type (avoids ClassCastException).
** 010 GES 20060208   @24391 Added a default format string getter and
**                           a new constructor that uses a format string
**                           to parse out a string value properly.
** 011 GES 20060312   @24987 Added variants of the OR, AND and NOT 
**                           operators to allow primitives to be passed
**                           in all possible combinations.
** 012 GES 20060417   @25556 Added default value generation.
** 013 GES 20060518   @26347 "/" is an invalid format string too.
** 014 GES 20060522   @26387 Added forms of the OR and AND operators which
**                           defer the processing of the right by passing
**                           a LogicalExpression instance which is only
**                           evaluated conditionally.  This is needed
**                           to ensure that right operand conditions that
**                           have side effects or can generate an error
**                           will not process if the left operand is
**                           enough to make a decision.
** 015 GES 20060616   @27357 OR and AND operators had unknown value 
**                           processing reversed from what it should have
**                           been (the logic was mis-documented originally
**                           and was implemented as mis-documented). This
**                           has been resolved.
** 016 GES 20060724   @28163 Added a forced assign() abstract method.
** 017 GES 20060807   @28475 Moved to externalizable interface to optimize
**                           network performance.
** 018 ECF 20060812   @28589 Added methods needed for database server-side
**                           function support.
** 019 NVS 20060908   @28589 compareTo now properly compares with String
**                           character type data.
** 020 GES 20061109   @31051 Added formatLength().
** 021 GES 20080624   @38913 Safer and more complete version of H019.
** 022 SIY 20080721   @39150 Fixed toString() behavior in order to match
**                           4GL behavior in various situations.
** 023 GES 20080911   @39791 Added assign(boolean) signature.
** 024 GES 20081001   @40035 Modified method names to shorten calling
**                           code for the logical operators.
** 025 ECF 20090212   @41301 Implemented a faster equals(). Handles most
**                           common cases without having to invoke the
**                           superclass' implementation.
** 026 GES 20090422   @41910 Converted to standard string formatting.
** 027 ECF 20090816   @43664 Removed final modifier from class.
** 028 GES 20090828   @43803 Make sure that ignore mode is disabled even if
**                           and exception occurs.
** 029 GES 20110303          Moved maximum/minimum to varargs.
** 030 CA  20130123          Added c'tor which builds a new instance from a
**                           BaseDataType value, if possible. This should be
**                           used only when constructing an instance using the
**                           value returned by a DYNAMIC-FUNCTION call; 4GL
**                           does some special casting in this case, which is
**                           not implemented yet.
** 031 GES 20130312          Implemented the BDT constructor. We hope it is suitable
**                           for any _POLY that returns a BDT which is supposed to
**                           be a logical.
** 032 GES 20130322          Fixed the BDT c'tor and modified the assign(BDT,boolean) to be the
**                           common location for the _POLY morphing. This is safe because all
**                           current usage would have generated a ClassCastException if that
**                           method was ever used with an invalid type. Now, instead of the CCE,
**                           the code will morph the value as is possible. The morphing code
**                           still needs to be checked.
** 033 MAG 20140602          Fixed the BDT c'tor and modified the assign(BDT, boolean) on _POLY
**                           morphing. Add BDT types on compareTo(Object).
**                           Improve compareTo(Object) by comparing unknown values.
** 034 CA  20150310          Fixed initialization of logical values from a string.
** 035 OM  20150630          Documented char-to-logical conversion quirk.
** 036 CA  20151222          Added instantiateDefaultExtent.
** 037 EVL 20160224          Javadoc fixes to make compatible with Oracle Java 8 for Solaris 10.
** 038 GES 20160309          Fixed fromString() to match new undocumented 4GL cases.
** 039 OM  20160302          Fixed logical(boolean) constructor.
** 040 GES 20160518          Switched from LogicalExpression anon instances to LogicalOp lambdas
**                           for AND and OR operator deferred evaluation.
** 041 GES 20160617          Added unknown literal processing for the polymorphic assign case.
** 042 CA  20160627          Reworked undoable support - the undoables register themselves with
**                           all blocks up the stack, until either 1. the tx block which created
**                           it is reached or 2. the last tx block where it was saved is reached.
** 043 GES 20171206          Changes in ErrorManager make silent error mode support unnecessary.
** 044 CA  20180514          Added logical(character, character) c'tor.
** 045 OM  20190206          Added implementation of field size needed by record-length.
** 046 CA  20190927          Added support for direct Java access from 4GL code.
** 047 RFB 20200804          _and() was evaluating the 2nd operator, instead of letting it flow to the and()
**                           method. This was causing issues if the 2nd operator was unnecessary, and would
**                           have side-effect results, like subscript out-of-range.
**     GES 20200806          Reduced ErrorManager context-local usage.
**     ME  20200810          Improvements to string parsing.
**     EVL 20200818          Fix for value creation issue from empty string for custom format case that
**                           considers empty string as valid false logical.
**     GES 20200820          Fix for fromString() "trash matching" mode and slight performance improvement.
** 048 IAS 20201007          Added Type enum
** 049 VVT 20210403          splitFormat() fixed: only one slash character is allowed. See #4880-67.
**     VVT 20210322          Fixed after the review. See #4880-107.
** 050 ME  20210504          Added isIncompatibleTypesOnConversion override for invalid POLY conversion.
**     CA  20210923          Fixed logical(BDT, fmt) builtin function.
**     OM  20220303          Renamed defaultFormat to DEFAULT_FORMAT and granted public access.
**                           General code maintenance.
**     AL2 20220319          Added value proxy check in assign.
** 051 CA  20230215          'duplicate()' method returns the real type instead of BDT.
** 052 CA  20231129          Avoid additional BDT creation for some operators which receive Java arguments.
** 053 CA  20240313          Converting a string to logical must not raise an error or set the  
**                           ERROR-STATUS:FLAG if the value does not match the format. 
** 054 CA  20240320          Avoid BDTs within internal FWD runtime.  Replaced iterators with Java 'for',  
**                           where it applies.
** 055 CA  20240324          Use logical constants for TRUE, FALSE, UNKNOWN, within internal FWD runtime.
**     CA  20240331          logical type checks must include sub-classes, too.
** 056 SP  20240415          Fixed assign(boolean): added missing checkUndoable().
*/

/*
** This program is free software: you can redistribute it and/or modify
** it under the terms of the GNU Affero General Public License as
** published by the Free Software Foundation, either version 3 of the
** License, or (at your option) any later version.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
** GNU Affero General Public License for more details.
**
** You may find a copy of the GNU Affero GPL version 3 at the following
** location: https://www.gnu.org/licenses/agpl-3.0.en.html
** 
** Additional terms under GNU Affero GPL version 3 section 7:
** 
**   Under Section 7 of the GNU Affero GPL version 3, the following additional
**   terms apply to the works covered under the License.  These additional terms
**   are non-permissive additional terms allowed under Section 7 of the GNU
**   Affero GPL version 3 and may not be removed by you.
** 
**   0. Attribution Requirement.
** 
**     You must preserve all legal notices or author attributions in the covered
**     work or Appropriate Legal Notices displayed by works containing the covered
**     work.  You may not remove from the covered work any author or developer
**     credit already included within the covered work.
** 
**   1. No License To Use Trademarks.
** 
**     This license does not grant any license or rights to use the trademarks
**     Golden Code, FWD, any Golden Code or FWD logo, or any other trademarks
**     of Golden Code Development Corporation. You are not authorized to use the
**     name Golden Code, FWD, or the names of any author or contributor, for
**     publicity purposes without written authorization.
** 
**   2. No Misrepresentation of Affiliation.
** 
**     You may not represent yourself as Golden Code Development Corporation or FWD.
** 
**     You may not represent yourself for publicity purposes as associated with
**     Golden Code Development Corporation, FWD, or any author or contributor to
**     the covered work, without written authorization.
** 
**   3. No Misrepresentation of Source or Origin.
** 
**     You may not represent the covered work as solely your work.  All modified
**     versions of the covered work must be marked in a reasonable way to make it
**     clear that the modified work is not originating from Golden Code Development
**     Corporation or FWD.  All modified versions must contain the notices of
**     attribution required in this license.
*/

package com.goldencode.p2j.util;

import java.io.*;
import java.math.*;
import java.util.*;
import java.util.function.*;

/**
 * A class that represents a Progress 4GL compatible logical object whose
 * data is mutable.  All Progress language features related to logical
 * types are supported including all function that can be accessed via the
 * logical operators.  In particular, the <code>AND</code>, <code>OR</code>
 * and <code>NOT</code> operators are implemented in this class (they are
 * unique to logicals) and all other logical operators are implemented in
 * the {@link CompareOps} class.
 * <p>
 * The only reason this class exists is to provide an object that represents 
 * 3 possible states: <code>true</code>, <code>false</code> and the
 * <code>unknown value</code>.  This is the only difference between the
 * Progress 4GL logical data type and the Java primitive <code>boolean</code>.
 * While a <code>java.lang.Boolean</code> could be used and set to 
 * <code>null</code> to indicate the <code>unknown value</code>, this
 * approach has the significant drawback of requiring unwrapping everywhere
 * and in addition, <code>null</code> checks are required wherever the
 * data is unwrapped.  This would require a very nasty bit of refactoring for
 * most expressions, which is made unnecessary by this class which represents
 * the tri-state of a logical using only internal means.  Since all operators
 * have been implemented as method calls and these methods are aware of the
 * <code>unknown value</code>, the resulting expressions are clean and
 * as close to the original level of expressiveness as possible. 
 * <p>
 * Format string related processing is handled in this class, see method
 * {@link #toString(String)}.
 * <p>
 * The following is the mapping of Progress language features to the
 * corresponding feature in this class:
 * <p>
 * <pre>
 * not      operator                       {@link #not} and {@link #_not}
 * and      operator                       {@link #and} and {@link #_and}
 * or       operator                       {@link #or} and {@link #_or}
 * =  or EQ operator                       {@link CompareOps#isEqual}
 * &lt;&gt; or NE operator                       {@link CompareOps#isNotEqual}
 * &gt;  or GT operator                       {@link CompareOps#isGreaterThan}
 * &gt;= or GE operator                       {@link CompareOps#isGreaterThanOrEqual}
 * &lt;  or LT operator                       {@link CompareOps#isLessThan}
 * &lt;= or LE operator                       {@link CompareOps#isLessThanOrEqual}
 * maximum  function                       {@link CompareOps#maximum(BaseDataType[])}
 * minimum  function                       {@link CompareOps#minimum(BaseDataType[])}
 * </pre> 
 * <p>
 * <pre>
 *     OR Operator Truth Table
 *
 *   Left       Right     Result
 * ---------  ---------  ---------
 * true       true       true
 * false      true       true
 * unknown    true       true
 * true       false      true
 * false      false      false
 * unknown    false      unknown
 * true       unknown    true
 * false      unknown    unknown
 * unknown    unknown    unknown
 * </pre>
 * <p>
 * <pre>
 *    AND Operator Truth Table
 *
 *   Left       Right     Result
 * ---------  ---------  ---------
 * true       true       true
 * false      true       false
 * unknown    true       unknown
 * true       false      false
 * false      false      false
 * unknown    false      false
 * true       unknown    unknown
 * false      unknown    false
 * unknown    unknown    unknown
 * </pre>
 * <p>
 * <pre>
 *    NOT Operator Truth Table
 *
 *  Operand    Result
 * ---------  ---------
 * true       false
 * false      true
 * unknown    unknown
 * </pre>
 * <p>
 * There are convenience versions of each operator that directly return
 * <code>boolean</code> values such that unwrapping is not needed.  These
 * are named the same as the operator methods above except there is no
 * 'Operator' appended.  For example, the not operator is {@link #not}.
 *
 * @author    GES
 */
public class logical
extends BaseDataType
{
   /** Singleton and immutable for the logical TRUE value. */
   public static final logical TRUE = new logicalConstant(true);

   /** Singleton and immutable for the logical FALSE value. */
   public static final logical FALSE = new logicalConstant(false);

   /** Singleton and immutable for the logical UNKNOWN value. */
   public static final logical UNKNOWN = new logicalConstant();
   
   /** The default format string. */
   public static final String DEFAULT_FORMAT = "yes/no";
   
   /**
    * Stores the state of this logical as <code>true</code> or 
    * <code>false</code>, independent of the state of whether or not this
    * instance represents the <code>unknown value</code>.
    */
   private boolean value = false;
   
   /**
    * Stores the state of whether or not this instance represents the
    * <code>unknown value</code>, independent of the state of this logical's
    * value as <code>true</code> or <code>false</code>.
    */
   private boolean unknown = false;
   
   /**
    * Default constructor, creates an instance that represents the unknown
    * value.
    */
   public logical()
   {
      unknown = true;
   }

   /**
    * This is a special c'tor which should be used only when converting the
    * value returned by a function or method with polymorphic return type into the
    * expected type (i.e. DYNAMIC-FUNCTION()).  In such cases, the 4GL does some
    * automatic type conversion (see {@link #assign(BaseDataType)}).
    * 
    * @param    value
    *           The value to be used for this instance.
    */
   public logical(BaseDataType value)
   {
      if (value == null || value.isUnknown())
      {
         setUnknown();
      }
      else
      {
         assign(value);
      }
   }

   /**
    * This is a special c'tor which should be used only when converting the
    * value returned by a function or method with polymorphic return type into the
    * expected type (i.e. DYNAMIC-FUNCTION()).  In such cases, the 4GL does some
    * automatic type conversion (see {@link #assign(BaseDataType)}).
    * 
    * @param    value
    *           The value to be used for this instance.
    * @param    fmt
    *           The format string to use.
    */
   public logical(BaseDataType value, character fmt)
   {
      if (value == null || value.isUnknown() || fmt.isUnknown())
      {
         setUnknown();
      }
      else if (value instanceof Text)
      {
         assign(new logical(((Text) value).getValue(), fmt.toStringMessage()));
      }
      else
      {
         assign(value);
      }
   }

   /**
    * This is a special c'tor which should be used only when converting the
    * value returned by a function or method with polymorphic return type into the
    * expected type (i.e. DYNAMIC-FUNCTION()).  In such cases, the 4GL does some
    * automatic type conversion (see {@link #assign(BaseDataType)}).
    * 
    * @param    value
    *           The value to be used for this instance.
    * @param    fmt
    *           The format string to use.
    */
   public logical(BaseDataType value, String fmt)
   {
      if (value == null || value.isUnknown() || fmt == null)
      {
         setUnknown();
      }
      else if (value instanceof Text)
      {
         assign(new logical(((Text) value).getValue(), fmt));
      }
      else
      {
         assign(value);
      }
   }
   
   /**
    * Constructs an instance that has the <code>boolean</code> value passed
    * in and which <b>does not</b> represent the <code>unknown value</code>. 
    *
    * @param    value
    *           The logical value of the resulting instance.
    */
   public logical(boolean value)
   {
      this.value = value;
   }
   
   /**
    * Constructs an instance that has the <code>boolean</code> value and
    * <code>unknown value</code> that exactly matches that of the passed-in 
    * instance.
    *
    * @param    value
    *           The logical and unknown value of the resulting instance.
    */
   public logical(logical value)
   {
      assign(value);
   }
   
   /**
    * Converts the given string into a logical value. A '?' is interpreted as
    * the <code>unknown value</code> and the strings 'yes' and 'true' (and
    * any abbreviations thereof) are considered <code>true</code> and
    * any other input is considered <code>false</code>.
    *
    * @param    value
    *           The text representation of the logical value.
    */
   public logical(String value)
   {
      this(value, DEFAULT_FORMAT);
   }
   
   /**
    * Converts the given string into a logical value. A '?' is interpreted as
    * the <code>unknown value</code> and the strings 'yes' and 'true' (and
    * any abbreviations thereof) are considered <code>true</code> and
    * any other input is considered <code>false</code>.
    *
    * @param    value
    *           The text representation of the logical value.
    */
   public logical(character value)
   {
      this(value, DEFAULT_FORMAT);
   }
   
   /**
    * Converts the given string into a logical value. A '?' is interpreted as
    * the <code>unknown value</code> and the strings 'yes' and 'true' (and
    * any abbreviations thereof) are considered <code>true</code> and
    * any other input is considered <code>false</code>.
    * <p>
    * Parses the string using default formats 'yes/no' and 'true/false' and
    * the passed in format string. Any any abbreviations of the above formats
    * are also considered as a match.
    * 
    * TODO: when a LOGICAL argument is passed as OUTPUT parameter to a procedure the implicit 
    *       conversion will fails without reason. The following message is displayed:
    *       [** Input value:  should be yes/no. (87)]
    *       When the argument is passes to a INPUT-OUTPUT parameter, everything is fine.
    *
    * @param    value
    *           The text representation of the logical value.
    * @param    fmt
    *           The format string to use.
    */
   public logical(character value, String fmt)
   {
      if (value.isUnknown())
      {
         setUnknown();
      }
      else
      {
         assign(new logical(value.getValue(), fmt));
      }
   }
   
   /**
    * Converts the given string into a logical value. A '?' is interpreted as
    * the <code>unknown value</code> and the strings 'yes' and 'true' (and
    * any abbreviations thereof) are considered <code>true</code> and
    * any other input is considered <code>false</code>.
    * <p>
    * Parses the string using default formats 'yes/no' and 'true/false' and
    * the passed in format string. Any any abbreviations of the above formats
    * are also considered as a match.
    * 
    * TODO: when a LOGICAL argument is passed as OUTPUT parameter to a procedure the implicit 
    *       conversion will fails without reason. The following message is displayed:
    *       [** Input value:  should be yes/no. (87)]
    *       When the argument is passes to a INPUT-OUTPUT parameter, everything is fine.
    *
    * @param    value
    *           The text representation of the logical value.
    * @param    fmt
    *           The format string to use.
    */
   public logical(character value, character fmt)
   {
      if (value.isUnknown() || fmt.isUnknown())
      {
         setUnknown();
      }
      else
      {
         assign(new logical(value.getValue(), fmt.toStringMessage()));
      }
   }
   
   /**
    * Converts the given string into a logical value. A '?' is interpreted as
    * the <code>unknown value</code>.  Parses the string using default 
    * formats 'yes/no' and 'true/false' and the passed in format string. Any
    * any abbreviations of the above formats are also considered as a match.
    *
    * @param    value
    *           The text representation of the logical value.
    * @param    fmt
    *           The format string to use.
    *
    * @throws   ErrorConditionException
    *           If no match is found.
    */
   public logical(String value, String fmt)
   throws ErrorConditionException
   {
      if (value == null || value.equals("?"))
      {
         setUnknown();
      }
      else
      {
         Boolean res = fromString(value, fmt);
         
         if (res == null)
         {
            String errmsg = "Input value: " + value + " should be " + fmt;
            ErrorManager.recordOrShowError(87, errmsg, true, true, false, false);
            
            setUnknown();
         }
         else
         {
            this.value = res;
         }
      }
   }
   
   /**
    * Constructs an instance after copying the parameter's data into the
    * internal representation of this class.
    * <p>
    * If the parameter is <code>null</code>, this instance will represent
    * the <code>unknown value</code>.
    *
    * @param   value
    *          The value to be used for this instance.
    */
   public logical(Boolean value)
   {
      if (value == null)
      {
         setUnknown();
      }
      else
      {
         this.value = value;
      }
   }
   
   /**
    * Resolve the given boolean value to a logical TRUE/FALSE singleton.
    * <p>
    * WARNING: this must be used only from within the fwd runtime or as an instance returned to the converted 
    * code, to be assigned to a mutable instance.  The return instance is immutable!
    * 
    * @param    value
    *           The value to resolve
    *           
    * @return   See above.
    */
   public static logical of(boolean value)
   {
      return value ? logical.TRUE : logical.FALSE;
   }
   
   /**
    * Check if the given value matches the received format.  This method is called at runtime
    * (from this class' constructor) or at conversion time (used for "boolean manhandling").
    * <p>
    * The default formats of "yes/no" and "true/false" are always considered and will match
    * in preference to an explicitly provided format string. This means that any conflict with
    * the explicitly provided format string will match one of the default formats first (in
    * preference).
    * <p>
    * Matching is done on a case-insensitive basis.
    * <p>
    * Interestingly, any matching subset of valid match text will match.  This means that an
    * exact match or an unambiguous abbreviated match to a format string of the form 'XXX/YYY'
    * will make x, X, xx, XX, xxx, XXX all resolve to <code>true</code> and y, Y, yy, YY, yyy,
    * YYY all resolve to <code>false</code>.  This optional abbreviation support works for
    * matches to both the default formats AND to explicitly provided custom formats.
    * <p>
    * The default formats have an additional "trash matching" behavior. When specifying yes, no,
    * true or false, the string can contain any trash so long as the trash is following a space
    * character.  This means a <code>yes   . bogus text.</code> matches a <code>yes</code> in a
    * default format. This same ridiculous trick does not work for explicit custom formats.
    * <p>
    * All of the above behavior is indeed how the 4GL does it.  No, it doesn't make any sense.
    * <p>
    * At conversion time, all enclosing quote characters should already have been removed from
    * both input parameters.  It is expected that this is always already the case with runtime
    * strings.
    * 
    * @param    val
    *           The value to be checked.
    * @param    fmt
    *           The format; if <code>null</code>, the {@link #DEFAULT_FORMAT} will be used.
    *           
    * @return   <code>null</code> if the value does not match the format.  Otherwise, the value's
    *           <code>true</code> or <code>false</code> state.
    */
   public static Boolean fromString(String val, String fmt)
   {
      // the val can be empty if the custom format case considers this option as valid boolean
      if (val == null || (val.isEmpty() && (fmt == null || (!fmt.startsWith("/") && !fmt.endsWith("/")))))
      {
         return null;
      }
      
      List<String> list = new ArrayList<>();
      
      // custom format is checked first (might be invalid, #errno 74)
      if (fmt != null)
      {
         fmt = fmt.toLowerCase();
         list.add(fmt);
      } 
      
      if (fmt == null || !fmt.equals(DEFAULT_FORMAT)) 
      {
         list.add(DEFAULT_FORMAT);
      }
      
      if (fmt == null || !fmt.equals("true/false")) 
      {
         list.add("true/false");
      }
      
      String[] fmts   = list.toArray(new String[0]);
      String   target = val.toLowerCase();
      
      for (int i = 0; i < fmts.length; i++)
      {
         String current  = fmts[i];
         String[] values = splitFormat(current);
         String yesVal   = values[0];
         String noVal    = values[1];
         
         // check 1: exact or unambiguous subset match
         if (target.isEmpty())
         {
            // in custom format case the target can be empty
            // for this  case one of the custom option should be empty too
            if (yesVal.isEmpty())
            {
               return true;
            }
            else if (noVal.isEmpty())
            {
               return false;
            }
         }
         else
         {
            if (yesVal.startsWith(target))
            {
               return true;
            }
            else if (noVal.startsWith(target))
            {
               return false;
            }
         }
         
         // default formats only, try trash matching mode
         if (fmt == null || fmts.length == 2 || i > 0)
         {
            // check 2: if not explicit format, first token in target (using space as separator) 
            // must be a yesVal or noVal. any other tokens after this one are discarded/ignored
            if (target.startsWith(yesVal + " "))
            {
               return true;
            }
            else if (target.startsWith(noVal + " "))
            {
               return false;
            }
         }
      }

      return null;
   }
   
   /**
    * Get the type
    * @return type
    */
   public Type getType()
   {
      return Type.LOGICAL;
   }

   /**
    * Returns the largest instance (<code>false</code> is smaller than
    * <code>true</code>) from the list.  This list may not include
    * <code>null</code> values.
    *
    * @param    list
    *           The list of logicals to check.
    *
    * @return   The largest instance or <code>unknown value</code> if any
    *           entries in the list are unknown or <code>null</code> if
    *           an empty list is passed.
    */
   public static logical maximum(logical ... list)   
   {
      return (logical) CompareOps.maximum(list);
   }
      
   /**
    * Returns the smallest instance (<code>false</code> is smaller than
    * <code>true</code>) from the list.  This list may not include
    * <code>null</code> values.
    *
    * @param    list
    *           The list of decimals to check.
    *
    * @return   The smallest instance or <code>unknown value</code> if any
    *           entries in the list are unknown or <code>null</code> if
    *           an empty list is passed.
    */
   public static logical minimum(logical ... list)   
   {
      return (logical) CompareOps.minimum(list);
   }   
   
   /**
    * Implements the <code>NOT</code> logical operator with the convenience
    * of converting the result to a primitive <code>boolean</code>. If the
    * result is the <code>unknown value</code>, this will be converted to a
    * <code>false</code>.
    * 
    * @param    op
    *           The operand.
    *
    * @return   The result of the operator.
    */
   public static boolean _not(logical op)
   {
      return op.unknown ? false : !op.value;
   }
   
   /**
    * Implements the <code>NOT</code> logical operator using the Java logical
    * NOT.
    * 
    * @param    op
    *           The operand.
    *
    * @return   The result of the operator.
    */
   public static logical not(boolean op)
   {
      return logical.of(!op);
   }

   /**
    * Implements the <code>NOT</code> logical operator with proper processing
    * of the <code>unknown value</code>.  In particular, if the operand
    * is unknown, then <code>unknown value</code> is returned.
    * <p>
    * If the operand is not <code>unknown</code>, the boolean value will
    * be negated and returned using the Java logical NOT.
    * 
    * @param    op
    *           The operand.
    *
    * @return   The result of the operator.
    */
   public static logical not(logical op)
   {
      if (op.unknown)
         return (logical) logical.UNKNOWN;
      
      return logical.of(!(op.value));
   }

   /**
    * Implements the <code>AND</code> logical operator with the convenience
    * of converting the result to a primitive <code>boolean</code>.
    * <p>
    * <b>Warning: this form requires that both operand expressions are 
    * evaluated in the context of the caller.  It does not maintain the 
    * standard semantic of a logical operator where the right operand is not
    * evaluated unless the left operand requires it.</b>  
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static boolean _and(boolean op1, boolean op2)
   {
      return op1 && op2;
   }
   
   /**
    * Implements the <code>AND</code> logical operator with the convenience
    * of converting the result to a primitive <code>boolean</code>. If the
    * result is the <code>unknown value</code>, this will be converted to a
    * <code>false</code>.
    * <p>
    * <b>Warning: this form requires that both operand expressions are 
    * evaluated in the context of the caller.  It does not maintain the 
    * standard semantic of a logical operator where the right operand is not
    * evaluated unless the left operand requires it.</b>  
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static boolean _and(logical op1, boolean op2)
   {
      return op2 && !op1.unknown && op1.value;
   }
   
   /**
    * Implements the <code>AND</code> logical operator with the convenience
    * of converting the result to a primitive <code>boolean</code>. If the 
    * result is the <code>unknown value</code>, this will be converted to a
    * <code>false</code>.
    * <p>
    * <b>Warning: this form requires that both operand expressions are 
    * evaluated in the context of the caller.  It does not maintain the 
    * standard semantic of a logical operator where the right operand is not
    * evaluated unless the left operand requires it.</b>  
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static boolean _and(boolean op1, logical op2)
   {
      return op1 && !op2.unknown && op2.value;
   }
   
   /**
    * Implements the <code>AND</code> logical operator with the convenience
    * of converting the result to a primitive <code>boolean</code>. If the 
    * result is the <code>unknown value</code>, this will be converted to a
    * <code>false</code>.
    * <p>
    * <b>Warning: this form requires that both operand expressions are 
    * evaluated in the context of the caller.  It does not maintain the 
    * standard semantic of a logical operator where the right operand is not
    * evaluated unless the left operand requires it.</b>  
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static boolean _and(logical op1, logical op2)
   {
      return !op1.unknown && !op2.unknown && op1.value && op2.value;
   }
   
   /**
    * Implements the <code>AND</code> logical operator with the convenience
    * of converting the result to a primitive <code>boolean</code>. If the 
    * result is the <code>unknown value</code>, this will be converted to a
    * <code>false</code>.
    * <p>
    * This form of the method allows the original semantic of the operator
    * to be maintained.  In particular, the expression defining the right
    * operand will not be evaluated unless the left operand does not fail
    * the logical test.
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static boolean _and(boolean op1, LogicalOp op2)
   {
      return op1 && _and(op1, op2.evaluate());
   }
   
   /**
    * Implements the <code>AND</code> logical operator with the convenience
    * of converting the result to a primitive <code>boolean</code>. If the 
    * result is the <code>unknown value</code>, this will be converted to a
    * <code>false</code>.
    * <p>
    * This form of the method allows the original semantic of the operator
    * to be maintained.  In particular, the expression defining the right
    * operand will not be evaluated unless the left operand does not fail
    * the logical test.
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static boolean _and(logical op1, LogicalOp op2)
   {
      return !op1.unknown && op1.value && _and(op1, op2.evaluate());
   }
   
   /**
    * Implements the <code>AND</code> logical operator (just a convenience
    * method for the Java logical AND).
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static logical and(boolean op1, boolean op2)
   {
      return logical.of(op1 && op2);
   }
   
   /**
    * Implements the <code>AND</code> logical operator with proper processing
    * of the <code>unknown value</code>.
    * <p>
    * If one operand is <code>unknown</code>, then <code>unknown</code>
    * is returned if the other operand is <code>true</code> and 
    * <code>false</code> is returned if the other operand is 
    * <code>false</code>.  If both operands are <code>unknown</code>, then
    * <code>unknown</code> is returned.
    * <p>
    * If no operand is <code>unknown</code>, the boolean values of each
    * logical are tested using the Java logical AND.
    * <p>
    * <b>Warning: this form requires that both operand expressions are 
    * evaluated in the context of the caller.  It does not maintain the 
    * standard semantic of a logical operator where the right operand is not
    * evaluated unless the left operand requires it.</b>  
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static logical and(boolean op1, logical op2)
   {
      return and(logical.of(op1), op2);
   }
   
   /**
    * Implements the <code>AND</code> logical operator with proper processing
    * of the <code>unknown value</code>.
    * <p>
    * If one operand is <code>unknown</code>, then <code>unknown</code>
    * is returned if the other operand is <code>true</code> and 
    * <code>false</code> is returned if the other operand is 
    * <code>false</code>.  If both operands are <code>unknown</code>, then
    * <code>unknown</code> is returned.
    * <p>
    * If no operand is <code>unknown</code>, the boolean values of each
    * logical are tested using the Java logical AND.
    * <p>
    * <b>Warning: this form requires that both operand expressions are 
    * evaluated in the context of the caller.  It does not maintain the 
    * standard semantic of a logical operator where the right operand is not
    * evaluated unless the left operand requires it.</b>  
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static logical and(logical op1, boolean op2)
   {
      return and(op1, logical.of(op2));
   }
   
   /**
    * Implements the <code>AND</code> logical operator with proper processing
    * of the <code>unknown value</code>.
    * <p>
    * If one operand is <code>unknown</code>, then <code>unknown</code>
    * is returned if the other operand is <code>true</code> and 
    * <code>false</code> is returned if the other operand is 
    * <code>false</code>.  If both operands are <code>unknown</code>, then
    * <code>unknown</code> is returned.
    * <p>
    * If no operand is <code>unknown</code>, the boolean values of each
    * logical are tested using the Java logical AND.
    * <p>
    * <b>Warning: this form requires that both operand expressions are 
    * evaluated in the context of the caller.  It does not maintain the 
    * standard semantic of a logical operator where the right operand is not
    * evaluated unless the left operand requires it.</b>  
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static logical and(logical op1, logical op2)
   {
      if (op1.unknown && op2.unknown)
      {
         return logical.UNKNOWN;
      }
      
      if (op1.unknown && !op2.unknown)
      {
         return op2.value ? logical.UNKNOWN : logical.of(false);
      }
      
      if (!op1.unknown && op2.unknown)
      {
         return op1.value ? logical.UNKNOWN : logical.of(false);
      }

      return logical.of(op1.value && op2.value);
   }

   /**
    * Implements the <code>AND</code> logical operator with proper processing
    * of the <code>unknown value</code>.
    * <p>
    * If one operand is <code>unknown</code>, then <code>unknown</code>
    * is returned if the other operand is <code>true</code> and 
    * <code>false</code> is returned if the other operand is 
    * <code>false</code>.  If both operands are <code>unknown</code>, then
    * <code>unknown</code> is returned.
    * <p>
    * If no operand is <code>unknown</code>, the boolean values of each
    * logical are tested using the Java logical AND.
    * <p>
    * This form of the method allows the original semantic of the operator
    * to be maintained.  In particular, the expression defining the right
    * operand will not be evaluated unless the left operand does not fail
    * the logical test.
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static logical and(boolean op1, LogicalOp op2)
   {
      // ensure that the right operand will not be evaluated unless the
      // left operand is true
      if (!op1)
      {
         // if the left operand is false, it doesn't matter if the right
         // operand is unknown, we always return false
         return logical.of(false);
      }
      
      return and(op1, op2.evaluate());
   }
   
   /**
    * Implements the <code>AND</code> logical operator with proper processing
    * of the <code>unknown value</code>.
    * <p>
    * If one operand is <code>unknown</code>, then <code>unknown</code>
    * is returned if the other operand is <code>true</code> and 
    * <code>false</code> is returned if the other operand is 
    * <code>false</code>.  If both operands are <code>unknown</code>, then
    * <code>unknown</code> is returned.
    * <p>
    * If no operand is <code>unknown</code>, the boolean values of each
    * logical are tested using the Java logical AND.
    * <p>
    * This form of the method allows the original semantic of the operator
    * to be maintained.  In particular, the expression defining the right
    * operand will not be evaluated unless the left operand does not fail
    * the logical test.
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static logical and(logical op1, LogicalOp op2)
   {
      // ensure that the right operand will not be evaluated unless the
      // left operand is true or UNKNOWN
      if (!op1.isUnknown() && !op1.value)
      {
         // if the left operand is false, it doesn't matter if the right
         // operand is unknown, we always return false
         return logical.of(false);
      }
      
      return and(op1, op2.evaluate());
   }
   
   /**
    * Implements the <code>OR</code> logical operator with the convenience
    * of converting the result to a primitive <code>boolean</code>.
    * <p>
    * <b>Warning: this form requires that both operand expressions are 
    * evaluated in the context of the caller.  It does not maintain the 
    * standard semantic of a logical operator where the right operand is not
    * evaluated unless the left operand requires it.</b>  
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static boolean _or(boolean op1, boolean op2)
   {
      return op1 || op2;
   }
   
   /**
    * Implements the <code>OR</code> logical operator with the convenience
    * of converting the result to a primitive <code>boolean</code>. If the
    * result is the <code>unknown value</code>, this will be converted to a
    * <code>false</code>.
    * <p>
    * <b>Warning: this form requires that both operand expressions are 
    * evaluated in the context of the caller.  It does not maintain the 
    * standard semantic of a logical operator where the right operand is not
    * evaluated unless the left operand requires it.</b>  
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static boolean _or(logical op1, boolean op2)
   {
      return op2 || (!op1.unknown && op1.value);
   }
   
   /**
    * Implements the <code>OR</code> logical operator with the convenience
    * of converting the result to a primitive <code>boolean</code>. If the
    * result is the <code>unknown value</code>, this will be converted to a
    * <code>false</code>.
    * <p>
    * <b>Warning: this form requires that both operand expressions are 
    * evaluated in the context of the caller.  It does not maintain the 
    * standard semantic of a logical operator where the right operand is not
    * evaluated unless the left operand requires it.</b>  
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static boolean _or(boolean op1, logical op2)
   {
      return op1 || (!op2.unknown && op2.value);
   }
   
   /**
    * Implements the <code>OR</code> logical operator with the convenience
    * of converting the result to a primitive <code>boolean</code>. If the
    * result is the <code>unknown value</code>, this will be converted to a
    * <code>false</code>.
    * <p>
    * <b>Warning: this form requires that both operand expressions are 
    * evaluated in the context of the caller.  It does not maintain the 
    * standard semantic of a logical operator where the right operand is not
    * evaluated unless the left operand requires it.</b>  
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static boolean _or(logical op1, logical op2)
   {
      return (!op1.unknown && op1.value) || (!op2.unknown && op2.value);
   }
   
   /**
    * Implements the <code>OR</code> logical operator with the convenience
    * of converting the result to a primitive <code>boolean</code>. If the
    * result is the <code>unknown value</code>, this will be converted to a
    * <code>false</code>.
    * <p>
    * This form of the method allows the original semantic of the operator
    * to be maintained.  In particular, the expression defining the right
    * operand will not be evaluated unless the left operand does not fail
    * the logical test.
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static boolean _or(boolean op1, LogicalOp op2)
   {
      return op1 || _or(op1, op2.evaluate());
   }
   
   /**
    * Implements the <code>OR</code> logical operator with the convenience
    * of converting the result to a primitive <code>boolean</code>. If the
    * result is the <code>unknown value</code>, this will be converted to a
    * <code>false</code>.
    * <p>
    * This form of the method allows the original semantic of the operator
    * to be maintained.  In particular, the expression defining the right
    * operand will not be evaluated unless the left operand does not fail
    * the logical test.
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static boolean _or(logical op1, LogicalOp op2)
   {
      return (!op1.unknown && op1.value) || _or(op1, op2.evaluate());
   }
   
   /**
    * Implements the <code>OR</code> logical operator using the Java logical
    * OR.
    * <p>
    * <b>Warning: this form requires that both operand expressions are 
    * evaluated in the context of the caller.  It does not maintain the 
    * standard semantic of a logical operator where the right operand is not
    * evaluated unless the left operand requires it.</b>  
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static logical or(boolean op1, boolean op2)
   {
      return logical.of(op1 || op2);
   }
   
   /**
    * Implements the <code>OR</code> logical operator with proper processing
    * of the <code>unknown value</code>.
    * <p>
    * If one operand is <code>unknown</code>, then <code>unknown</code>
    * is returned if the other operand is <code>false</code> and 
    * <code>true</code> is returned if the other operand is 
    * <code>true</code>.  If both operands are <code>unknown</code>, then
    * <code>unknown</code> is returned.
    * <p>
    * If no operand is <code>unknown</code>, the boolean values of each
    * logical are tested using the Java logical OR.
    * <p>
    * <b>Warning: this form requires that both operand expressions are 
    * evaluated in the context of the caller.  It does not maintain the 
    * standard semantic of a logical operator where the right operand is not
    * evaluated unless the left operand requires it.</b>  
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static logical or(boolean op1, logical op2)
   {
      return or(logical.of(op1), op2);
   }
      
   /**
    * Implements the <code>OR</code> logical operator with proper processing
    * of the <code>unknown value</code>.
    * <p>
    * If one operand is <code>unknown</code>, then <code>unknown</code>
    * is returned if the other operand is <code>false</code> and 
    * <code>true</code> is returned if the other operand is 
    * <code>true</code>.  If both operands are <code>unknown</code>, then
    * <code>unknown</code> is returned.
    * <p>
    * If no operand is <code>unknown</code>, the boolean values of each
    * logical are tested using the Java logical OR.
    * <p>
    * <b>Warning: this form requires that both operand expressions are 
    * evaluated in the context of the caller.  It does not maintain the 
    * standard semantic of a logical operator where the right operand is not
    * evaluated unless the left operand requires it.</b>  
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static logical or(logical op1, boolean op2)
   {
      return or(op1, logical.of(op2));
   }
   
   /**
    * Implements the <code>OR</code> logical operator with proper processing
    * of the <code>unknown value</code>.
    * <p>
    * If one operand is <code>unknown</code>, then <code>unknown</code>
    * is returned if the other operand is <code>false</code> and 
    * <code>true</code> is returned if the other operand is 
    * <code>true</code>.  If both operands are <code>unknown</code>, then
    * <code>unknown</code> is returned.
    * <p>
    * If no operand is <code>unknown</code>, the boolean values of each
    * logical are tested using the Java logical OR.
    * <p>
    * <b>Warning: this form requires that both operand expressions are 
    * evaluated in the context of the caller.  It does not maintain the 
    * standard semantic of a logical operator where the right operand is not
    * evaluated unless the left operand requires it.</b>  
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static logical or(logical op1, logical op2)
   {
      if (op1.unknown && op2.unknown)
      {
         return logical.UNKNOWN;
      }
      
      if (op1.unknown && !op2.unknown)
      {
         return op2.value ? logical.of(true) : logical.UNKNOWN;
      }
      
      if (!op1.unknown && op2.unknown)
      {
         return op1.value ? logical.of(true) : logical.UNKNOWN;
      }
      
      return logical.of(op1.value || op2.value);
   }
   
   /**
    * Implements the <code>OR</code> logical operator with proper processing
    * of the <code>unknown value</code>.
    * <p>
    * If one operand is <code>unknown</code>, then <code>unknown</code>
    * is returned if the other operand is <code>false</code> and 
    * <code>true</code> is returned if the other operand is 
    * <code>true</code>.  If both operands are <code>unknown</code>, then
    * <code>unknown</code> is returned.
    * <p>
    * If no operand is <code>unknown</code>, the boolean values of each
    * logical are tested using the Java logical OR.
    * <p>
    * This form of the method allows the original semantic of the operator
    * to be maintained.  In particular, the expression defining the right
    * operand will not be evaluated unless the left operand does not fail
    * the logical test.
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static logical or(boolean op1, LogicalOp op2)
   {
      // ensure that the right operand will not be evaluated unless the
      // left operand is false or unknown
      if (op1)
      {
         return logical.of(true);
      }
      
      // unknown value processing is too complex to inline here, use the
      // common method even if it is a bit slower
      return or(logical.of(op1), op2.evaluate());
   }
      
   /**
    * Implements the <code>OR</code> logical operator with proper processing
    * of the <code>unknown value</code>.
    * <p>
    * If one operand is <code>unknown</code>, then <code>unknown</code>
    * is returned if the other operand is <code>false</code> and 
    * <code>true</code> is returned if the other operand is 
    * <code>true</code>.  If both operands are <code>unknown</code>, then
    * <code>unknown</code> is returned.
    * <p>
    * If no operand is <code>unknown</code>, the boolean values of each
    * logical are tested using the Java logical OR.
    * <p>
    * This form of the method allows the original semantic of the operator
    * to be maintained.  In particular, the expression defining the right
    * operand will not be evaluated unless the left operand does not fail
    * the logical test.
    * 
    * @param    op1
    *           The left operand.
    * @param    op2
    *           The right operand.
    *
    * @return   The result of the operator.
    */
   public static logical or(logical op1, LogicalOp op2)
   {
      // ensure that the right operand will not be evaluated unless the
      // left operand is false or unknown
      if (!op1.isUnknown() && op1.value)
      {
         return logical.of(true);
      }
      
      return or(op1, op2.evaluate());
   }
   
   /**
    * Split a valid logical format string in a safe way that handles all
    * possible edge cases. Examples:
    * <p>
    * <ul>        
    *    <li> an empty or <code>null</code> format string is invalid
    *    <li> a format that starts with '/' has an empty string for the
    *         <code>true</code> value
    *    <li> a format that ends with '/' or has no '/' has an empty string
    *         for the <code>false</code>
    *    <li> otherwise the format string is split into 2 pieces at the '/' 
    *         character and the left side is used as the <code>true</code>
    *         representation and the right side is the <code>false</code>
    * </ul>
    *
    * @param    fmt
    *           Format to split.
    *
    * @return   The split format string as a string array with 2 elements,
    *           where the first element is the <code>true</code> value
    *           and the second element is the <code>false</code> value.
    *           
    *           Return {@code null} if the provided format is invalid, and error was not thrown.
    *           
    * @throws   ErrorConditionException
    *           if the provided format is invalid (null, empty or a single slash character).
    *           The error code is 74.
    */
   public static String[] splitFormat(String fmt)
   throws ErrorConditionException
   {
      // interestingly, only the empty string or the "/" are problems
      if (fmt == null || fmt.length() == 0 || fmt.equals("/"))
      {
         ErrorManager.recordOrThrowError(74,
                  String.format("Value %s cannot be displayed using %s", "", fmt));
         return null;
      }
      
      // usually, format strings must have 2 non-empty parts separated by a '/' so let's look for that char
      final int split = fmt.indexOf('/');
      if (split < 0)
      {
         // edge case where there is no '/' at all, use the whole ftm as the true value
         return new String[] { fmt, "" };
      }
      
      // It is an error in OE if format has more than one slash character.
      final int secondSlashIndex = fmt.indexOf('/', split + 1);
      if (secondSlashIndex > 0)
      {
         ErrorManager.genInvalidCharError(secondSlashIndex, fmt);
         return null;
      }
      
      return new String[] { fmt.substring(0, split), fmt.substring(split + 1) };
   }
   
   /**
    * Determines the largest possible string length that can match either of
    * the specified values in a valid format string.  For example, if the
    * format string was specified as "Yep/Nope" then the largest size would
    * be returned as 4.  The format string will be split and the length of
    * the larger of the 2 values will be returned.
    *
    * @param    fmt
    *           A valid format string for the <code>logical</code> type.
    *
    * @return   The length of the longer of the 2 values in the format
    *           string.
    */
   public static int maximumStringSize(String fmt)
   {
      if (fmt == null)
      {
         fmt = "";
      }
      
      String[] result = splitFormat(fmt);
      
      if (result == null)
      {
         result = new String[] { "", "" };
      }
      
      return Math.max(result[0].length(), result[1].length());
   }
   
   /**
    * Calculate the length of a formatted value (the text form of the value)
    * using this format string.
    *
    * @param    fmt
    *           The format string.
    *
    * @return   The length in characters of the any resulting formatted
    *           value.
    */
   public int formatLength(String fmt)
   {
      if (fmt == null)
      {
         fmt = defaultFormatString();
      }
      
      return maximumStringSize(fmt);
   }
   
   /**
    * An equality test which handles the most common cases with the least
    * amount of overhead.  The superclass implementation is invoked otherwise.
    * <p>
    * This implementation is consistent with {@link #hashCode()}.
    * 
    * @see com.goldencode.p2j.util.BaseDataType#equals(java.lang.Object)
    */
   public boolean equals(Object o)
   {
      if (this == o)
      {
         return true;
      }
      
      if (o instanceof logical)
      {
         logical that = (logical) o;
         
         boolean u1 = this.unknown;
         boolean u2 = that.unknown;
         
         if (u1 && u2)
         {
            return true;
         }
         
         if (u1 || u2)
         {
            return false;
         }
         
         return (this.value == that.value);
      }
      
      return super.equals(o);
   }
   
   /**
    * Hash code implementation which is consistent with {@link
    * BaseDataType#equals}.
    *
    * @return  Hash code value for this object instance.
    */
   public int hashCode()
   {
      int result = 17;
      if (isUnknown())
      {
         return result;
      }
      
      result = 37 * result + (value ? 0 : 1);
      
      return result;
   }
   
   /**
    * Creates a new instance of the same type that represents the 
    * <code>unknown value</code>.
    *
    * @return   An instance that represents the <code>unknown value</code>.
    */
   public BaseDataType instantiateUnknown()   
   {
      return new logical();
   }
   
   /**
    * Creates a new instance of the same type that represents the 
    * default initialized value.
    *
    * @return   An instance that represents the default value.
    */
   public BaseDataType instantiateDefault()   
   {
      return new logical(false);
   }
   
   /**
    * Does the same as standard <code>clone()</code> method but returns an
    * instance of <code>BaseDataType</code> and doesn't throw the
    * <code>CloneNotSupportedException</code>.
    *
    * @return   A clone of this instance.  
    */
   public logical duplicate()
   {
      return new logical(this);
   }
   
   /**
    * Accesses the state of this instance's <code>boolean</code> value. If
    * this instance represents the <code>unknown value</code>, then this
    * method will return <code>false</code> even if the internal state is 
    * <code>true</code>!
    *
    * @return   The state of this instance's <code>boolean</code> value or
    *           <code>false</code> if this instance represents the
    *           <code>unknown value</code>.
    */
   public boolean booleanValue()
   {
      if (unknown)
         return false;
      
      return value;
   }
   
   /**
    * Determines if this instance represents the <code>unknown value</code>.
    *
    * @return   <code>true</code> if this instance is set to the
    *           <code>unknown value</code>.
    */
   public boolean isUnknown()
   {
      return unknown;
   }
   
   /**
    * Sets the state of this instance's <code>unknown value</code> flag to
    * <code>true</code>.
    * <p>
    * <b>Warning: a separate call is needed to ensure that the data of this
    * instance is set to the correct value.</b>
    */
   public void setUnknown()
   {
      if (!unknown)
      {
         checkUndoable(true);
      }
      
      unknown = true;
   }
   
   /**
    * Accesses the state of this instance's <code>boolean</code> value
    * independently of the state of whether this instance represents the
    * <code>unknown value</code>.    If this instance represents the
    * <code>unknown value</code>, the returned <code>boolean</code> is
    * <b>not valid</b>!
    *
    * @return   The state of this instance's <code>boolean</code> value.
    */
   public boolean getValue()
   {
      return value;
   }
   
   /**
    * Sets the state of this instance's <code>boolean</code> value
    * independently of the state of whether this instance represents the
    * <code>unknown value</code>.    This also sets the 
    * <code>unknown value</code> state for this instance to
    * <code>false</code>.
    *
    * @param    value
    *           The state to set this instance's <code>boolean</code> value.
    */
   public void setValue(boolean value)
   {
      if (unknown || value != this.value)
      {
         checkUndoable(true);
      }
      
      this.value = value;
      unknown    = false;
   }
   
   /**
    * Returns {@code true} if dynamic data type conversion should not be attempted, it can also throw an
    * {@code ErrorConditionException} in case of incompatible types for a POLY conversion.
    * (e.g. DYNAMIC-FUNCTION()).
    *
    * @throws   ErrorConditionException
    *           If dynamic conversion of input value is not supported.
    */
   @Override
   protected boolean isIncompatibleTypesOnConversion(BaseDataType value)
   {
      // invalid conversion is being thrown even if unknown
      if (value instanceof longchar /*|| value instanceof clob*/ || value instanceof blob) 
      {
         incompatibleTypesOnConversion();
      }
      
      return super.isIncompatibleTypesOnConversion(value);
   }
   
   /**
    * Sets the state (data and unknown value) of this instance based on the
    * state of the passed instance.
    * <p>
    * If the value is not of type <code>logical</code>, the following automatic type
    * conversions will occur:
    * <p>
    * <ol>
    *    <li> if the value is a logical value, the current value is returned</li>
    *    <li> if the value is unknown (including unknown literal), sets the instance to 
    *         unknown</li>
    *    <li> if the value is a non-unknown rowid or BinaryData (raw or memptr) value the string
    *         representation is converted to a logical value</li>
    *    <li> if the value is a non-unknown numeric value, returns a logical value set to true
    *         when the numeric value is not zero, false if the numeric value is 0</li>
    *    <li> if the value is a non-unknown character or longchar value, it attempts to convert
    *         the character value to a logical value (if the character is "yes", it is set to
    *         true, if is "no", it is set to false</li>
    *    <li> if the value is a non-unknown date or datetime it returns a logical false for a
    *         value of 31/12/-4714 and true for other values. Basically the number of days from
    *         1/1/4713 B.C. to that date are converted to logical value. If the number of days
    *         are 0 a false value is returned otherwise a true value is returned.</li>
    *    <li> if the value is a non-unknown handle or comhandle value, it returns a logical 
    *         false if the resource id is 0 and true if the resource id is not 0.</li>
    *    <li> else, it attempts to convert the value's string representation to logical</li>
    * </ol>
    * <p>
    * This variant is meant to handle the cases of built-in functions and methods in the 4GL
    * which have polymorphic return types (e.g. DYNAMIC-FUNCTION()). This should NOT be used for
    * non-polymorphic assignments.
    *
    * @param    value
    *           The instance from which to copy state.
    */
   public void assign(BaseDataType value)
   {
      if (value == null)
      {
         setUnknown();
         return;
      }
      
      // the value may be a proxy; make sure to unwrap and work with the real value
      value = value.val();
      if (value.isUnknown())
      {
         setUnknown();
      }
      else if (value instanceof logical)
      {
         assign((logical) value);
      }
      else if (value instanceof jobject)
      {
         assign((jobject<?>) value);
      }
      else
      {
         // this path is only used when type morphing is needed
         if (value instanceof date && !(value instanceof datetime))
         {
            // date values only
            long day = ((date) value).longValue();
            assign(day != 0);
         }
         else if (value instanceof handle)
         {
            Long id = ((handle) value).getResourceId();
            
            if (id != null)
            {
               assign(id != 0);
            }
            else
            {
               setUnknown();
            }
         }
         else if (value instanceof NumberType)
         {
            // decimal, integer, int64, recid
            BigDecimal decimalValue = ((NumberType) value).toBigDecimal();
            
            if (decimalValue == null)
            {
               setUnknown();
            }
            else
            {
               assign(decimalValue.signum() != 0);
            }
         }
         else if (value instanceof Text)
         {
            // yes/no character or longchar values can be converted
            assign(new logical(value.toStringMessage()));
         }
         else if (value instanceof raw)
         {
            setUnknown();
         }
         else
         {
            incompatibleTypesOnConversion();
         }
      }
   }
   
   /**
    * Sets the state (data and unknown value) of this instance based on the
    * state of the passed instance.
    *
    * @param    value
    *           The instance from which to copy state.
    */
   public void assign(logical value)
   {
      // the value may be a proxy; make sure to unwrap and work with the real value
      if (BaseDataType.isProxy(value))
      {
         assign(value.val());
         return;
      }
      checkUndoable(value);
      
      this.value = value.value;
      unknown    = value.unknown;
   }
   
   /**
    * Sets the state (data) of this instance based on the given value.
    *
    * @param    value
    *           The data from which to copy state.
    */
   public void assign(boolean value)
   {
      if (unknown || this.value != value)
      {
         checkUndoable(true);
      }
      
      this.value = value;
      unknown    = false;
   }
   
   /**
    * Sets the state (data and unknown value) of this instance based on the
    * state of the passed instance.
    *
    * @param    value
    *           The instance from which to copy state.
    */
   public void assign(Undoable value)
   {
      assign((logical) value);
   }
   
   /**
    * Compares this instance with the specified instance and returns a -1
    * if this instance is less than the specified, 0 if the two instances
    * are equal and 1 if this instance is greater than the specified
    * instance.  This is the implementation of the <code>Comparable</code>
    * interface.
    * <p>
    * The algorithm will fail to give meaningful results in the case where
    * one tries to sort against other objects that do not represent compatible
    * values.
    *
    * @param    obj
    *           The instance to compare against.
    *
    * @return   -1, 0 or 1 depending on if this instance is less than,
    *           equal to or greater (respectively) than the specified
    *           instance <code>obj</code>.
    */
   public int compareTo(Object obj)
   {
      logical l = null;
      
      if (obj instanceof logical)
      {
         l = (logical) obj;
      }
      else if (obj instanceof BaseDataType)
      {
         BaseDataType bdt = (BaseDataType) obj;

         if (isUnknown() && bdt.isUnknown())
         {
            return 0;
         }
         else if (isUnknown())
         {
            return -1;
         }
         else if (bdt.isUnknown())
         {
            return 1;
         }
         else
         {
            l = new logical(bdt);
            
             // An unknown value should be always converted to a unknown logical value.
             // A non-unknown value should be always converted to a non-unknown logical value.
             // If an unknown value is converted to a non-unknown value the conversion fails.
             // If a non-unknown value is converted to an unknown value the conversion fails.
            if (l.isUnknown() != bdt.isUnknown())
            {
               incompatibleTypesOnConversion();
            }
         }
      }
      else if (obj instanceof Boolean)
      {
         l = logical.of(((Boolean) obj).booleanValue());
      }
      else if (obj instanceof String)
      {
         l = convertString((String)obj);
         
         // if an error occurred, we detect it here and return
         if (l == null)
         {
            return -1;
         }
      }
      else
      {
         return -1;
      }
      
      int result = 0;
      
      if (!unknown && !l.unknown)
      {      
         if (value == l.value)
         {
            result = 0;
         }
         else if (!value && l.value)
         {
            result = -1;
         }
         else
         {
            result = 1;
         }
      }
      else
      {
         if (unknown == l.unknown)
         {
            result = 0;
         }
         else if (unknown)
         {
            result = -1;
         }
         else
         {
            result = 1;
         }
      }
         
      return result;
   }
   
   /**
    * Returns the larger (<code>false</code> is smaller than
    * <code>true</code>) of the current or passed-in instance.
    *
    * @param    l
    *           The instance to compare against.
    *
    * @return   The largest instance.
    */
   public logical maximum(logical l)
   {
      return (logical) super.maximum(l);
   }
   
   /**
    * Returns the smaller (<code>false</code> is smaller than
    * <code>true</code>) of the current or passed-in instance.
    *
    * @param    l
    *           The instance to compare against.
    *
    * @return   The smallest instance.
    */
   public logical minimum(logical l)
   {
      return (logical) super.minimum(l);
   }
   
   /**
    * Return the current value as a Java wrapper.
    *
    * @return  Current value or {@code null} if unknown.
    */
   public Boolean toJavaType()
   {
      return isUnknown() ? null : Boolean.valueOf(value);
   }
   
   /**
    * Creates a string representation of the instance data using the default Progress 4GL format of
    * {@code 'yes/no'}. If the instance represents the {@code unknown value}, a {@code '?'} will be returned.
    *
    * @return  A short string representation of the object.
    */
   public String toString()
   {
      return toString(null);
   }
   
   /**
    * Creates a string representation of the instance data in a form that is
    * compatible with the <code>MESSAGE</code> language statement.  If the
    * instance represents the <code>unknown value</code>, a '?' will be
    * returned.
    *
    * @return   The 'message' formatted string.
    */
   public String toStringMessage()
   {
      return toString(null);
   }
   
   /**
    * Creates a string representation of the instance data using the 'export'
    * format. For the logical data type this is the same as the default
    * format string of 'yes/no'.  If the instance represents the
    * <code>unknown value</code>, a '?' will be returned.
    *
    * @return   The 'export' formatted string.
    */
   public String toStringExport()
   {
      return toString(null);
   }
   
   /**
    * Creates a string representation of the instance data using the user-
    * specified Progress 4GL format string.  If the passed-in format is
    * <code>null</code>, then a default format string of 'yes/no' will be
    * used.  Please note that due to the implementation, it is faster
    * to use a <code>null</code> format string than to explicitly encode
    * 'yes/no'.  If the instance represents the <code>unknown value</code>,
    * a '?' will be returned.
    * <p>
    * The format string must be in the form of 'xxx/yyy' where xxx is the
    * text for a <code>true</code> and yyy is the text for a 
    * <code>false</code> value.  For example, one might want a 'true/false'
    * to be used instead of the default.  The user cannot override the '?'
    * returned for the <code>unknown value</code>.
    *
    * @param    fmt
    *           The Progress 4GL format string for a logical data type.
    *
    * @return   The formatted string.
    */
   public String toString(String fmt)   
   throws ErrorConditionException
   {
      // quick-out when unknown (no user override for that case)
      if (unknown)
      {
         return "?";
      }
      
      // implement 'default' behavior (as if the format string was "yes/no") 
      if (fmt == null)
      {
         return value ? "yes" : "no";
      }
      
      String[] result = splitFormat(fmt);
      if (result == null)
      {
         return "";
      }
      
      StringBuilder res = new StringBuilder(value ? result[0] : result[1]);
      int fmtLen = formatLength(fmt);
      
      while(res.length() < fmtLen)
      {
         res.append(' ');
      }
      
      // normal case
      return res.toString();
   }   
   
   /**
    * Return the default display format string for this type.
    *
    * @return   The default format string.
    */
   public String defaultFormatString()
   {
      return DEFAULT_FORMAT;
   }
   
   /**
    * Obtain the length (in bytes) of this BDT will use when serialized. 
    *
    * @return  the length of this BDT will use when serialized.
    */
   @Override
   public int getSize()
   {
      return (isUnknown() || !value) ? 1 : 2;
   }
   
   /**
    * Replacement for the default object reading method. The latest
    * state is read from the input source.
    * 
    * @param    in
    *           The input source from which fields will be restored.
    *
    * @throws   IOException
    *           In case of I/O errors.
    * @throws   ClassNotFoundException
    *           If payload can't be instantiated.
    */
   public void readExternal(ObjectInput in)
   throws IOException,
          ClassNotFoundException
   {
      value   = in.readBoolean();
      unknown = in.readBoolean();
   }

   /**
    * Replacement for the default object writing method. The latest
    * state is written to the output destination.
    * 
    * @param    out
    *           The output destination to which fields will be saved.
    *
    * @throws   IOException
    *           In case of I/O errors.
    */
   public void writeExternal(ObjectOutput out)
   throws IOException
   {
      out.writeBoolean(value);
      out.writeBoolean(unknown);
   }

   /**
    * Get the default initialization for an extent variable of this type.
    * 
    * @return   See above.
    */
   @Override
   protected BaseDataType instantiateDefaultExtent()
   {
      return logical.of(false);
   }

   /**
    * Helper to convert a text value into a logical value with ERROR
    * processing SUPPRESSED.  The only known instance where we use this is
    * in a validation expression, so the suppression of error processing
    * should be OK when it normally might be dangerous.
    *
    * @param    val
    *           The value to attempt to convert. If it does not match the
    *           string "yes" or "no", then an error would normally occur.
    *           This error will be suppressed, but the resulting failure
    *           will be detected.
    *
    * @return   The converted instance or <code>null</code> on any failure.
    */
   private logical convertString(String val)
   {
      logical[] l = new logical[1];
      
      try
      {
         ErrorManager.ignore(() -> l[0] = new logical(val));
      }
      
      catch (ErrorConditionException ece)
      {
         // should not happen but we put this here for safety
         return null;
      }
      
      // if an error silently occurred inside the logical constructor, we
      // detect it here and return
      if (l[0] != null && l[0].isUnknown())
      {
         l[0] = null;
      }
      
      return l[0];
   }
   
   /**
    * An immutable logical type, to be used for TRUE/FALSE/UNKNOWN singletons required within FWD runtime.
    * <p>
    * Instances of this type are serializable.
    */
   public static class logicalConstant
   extends logical
   implements BaseDataTypeConstant
   {
      /**
       * Default constructor, creates an instance that represents the unknown value.
       */
      public logicalConstant()
      {
         // unknown
      }
      
      /**
       * Constructs an instance that has the <code>boolean</code> value passed in and which <b>does not</b> 
       * represent the <code>unknown value</code>. 
       *
       * @param    value
       *           The logical value of the resulting instance.
       */
      public logicalConstant(boolean value)
      {
         super(value);
      }
      
      /**
       * Operation not possible.
       * 
       * @throws   UnsupportedOperationException
       *           This is an immutable logical instance.
       */
      @Override
      public void setUnknown()
      {
         throw new UnsupportedOperationException("This is an immutable logical instance.");
      }
      
      /**
       * Operation not possible.
       * 
       * @throws   UnsupportedOperationException
       *           This is an immutable logical instance.
       */
      @Override
      public void setValue(boolean value)
      {
         throw new UnsupportedOperationException("This is an immutable logical instance.");
      }
      
      /**
       * Operation not possible.
       * 
       * @throws   UnsupportedOperationException
       *           This is an immutable logical instance.
       */
      @Override
      public void assign(BaseDataType value)
      {
         throw new UnsupportedOperationException("This is an immutable logical instance.");
      }
      
      /**
       * Operation not possible.
       * 
       * @throws   UnsupportedOperationException
       *           This is an immutable logical instance.
       */
      @Override
      public void assign(boolean value)
      {
         throw new UnsupportedOperationException("This is an immutable logical instance.");
      }
      
      /**
       * Operation not possible.
       * 
       * @throws   UnsupportedOperationException
       *           This is an immutable logical instance.
       */
      @Override
      public void assign(jobject<?> value)
      {
         throw new UnsupportedOperationException("This is an immutable logical instance.");
      }
      
      /**
       * Operation not possible.
       * 
       * @throws   UnsupportedOperationException
       *           This is an immutable logical instance.
       */
      @Override
      public void assign(logical value)
      {
         throw new UnsupportedOperationException("This is an immutable logical instance.");
      }
      
      /**
       * Operation not possible.
       * 
       * @throws   UnsupportedOperationException
       *           This is an immutable logical instance.
       */
      @Override
      public void assign(Object value)
      {
         throw new UnsupportedOperationException("This is an immutable logical instance.");
      }
      
      /**
       * Operation not possible.
       * 
       * @throws   UnsupportedOperationException
       *           This is an immutable logical instance.
       */
      @Override
      public void assign(Undoable value)
      {
         throw new UnsupportedOperationException("This is an immutable logical instance.");
      }
      
      /**
       * Operation not possible.
       * 
       * @throws   UnsupportedOperationException
       *           This is an immutable logical instance.
       */
      @Override
      Supplier<AbstractParameter> getAssigner()
      {
         throw new UnsupportedOperationException("This is an immutable logical instance.");
      }
   }
}