Operator = (comparison) Foundation

Simple equality operator (binary): testing two values for equality.

<Expression1> = <Expression2>
<Expression1> and <Expression2> are expressions of the same data type or the value NIL. The values of the two expressions are tested for equality. Each data type can be tested for equal NIL.

The simple equality operator compares two values of the same data type and returns the result of the comparison as a logical value. The result is .T. (true) only when the value of <Expression1> equals the value of <Expression2>. Otherwise it is .F. (false).

Comparison with NIL

The equals operator can compare values of all data types (including array, code block and object) with the value NIL. In this case, the value .T. (true) is returned only when both expressions are equal to NIL.

Comparison of characters

The settings of SET EXACT ON | OFF and SET LEXICAL ON | OFF are taken into account in comparing characters or character strings (see example). When SET LEXICAL is set to OFF, characters are compared with each other based on the collation table specified via the SET COLLATION command.

With SET EXACT OFF, the characters are compared up to the length of the right character string <Expression2>. With SET EXACT ON, the characters are compared up to the length of the left character string <Expression1> and trailing blanks are not considered. If <Expression2> contains a null string (""), the simple equal operator always returns the value .T. (true) with SET EXACT OFF, and always returns the value .F. (false) with SET EXACT ON unless both operands contain a null string.

The setting SET LEXICAL ON has precedence over SET EXACT ON. When SET LEXICAL ON, character comparisons are based on the country specific lexical character values defined by the operating system. The lexical value of one or more characters can be redefined with the function SetLexrule().

Comparison of date values

Values with data type date are compared on a chronological basis.

Comparison of logical values

The value .F. (false) is not equal to the value .T. (true).

Comparison of numeric values

The comparison is based on the sizes of the numeric values.

The simple equality operator (=)
// This example illustrates the results of the simple 
// equality operator with various comparison expressions. 
// The character string comparisons show the various possibilities of 
// using SET EXACT and SET LEXICAL. 

                                    // character value 
   ? "A"  = "Z"                     // result: .F. 
   ? "A"  = "A "                    // result: .F. 
   ? "A " = "A"                     // result: .T. 
   ? ""   = "A"                     // result: .F. 
   ? "A"  = ""                      // result: .T. 
   ? "AB" = "ABC"                   // result: .F. 
   ? "ABC"= "AB"                    // result: .T. 


   ? "A"  = "Z"                     // result: .F. 
   ? "A"  = "A "                    // result: .T. 
   ? "A " = "A"                     // result: .T. 
   ? ""   = "A"                     // result: .F. 
   ? "A"  = ""                      // result: .F. 
   ? "AB" = "ABC"                   // result: .F. 
   ? "ABC"= "AB"                    // result: .F. 

   SetLexrule( "ß", "ss" )          // "ß" translates to "ss" 
   ? "gross" = "groß"               // result: .F. 

   ? "gross" = "groß"               // result: .T. 

   ? CtoD("12/31/94") = ;           // date value 
     CtoD("01/01/95")               // result: .F. 

                                    // logical value 
   ? .F. = .T.                      // result: .F. 

                                    // numeric value 
   ? 5 = 10                         // result: .F. 
   ? 10 = 5                         // result: .F. 

                                    // array 
   ? {1,2,3} = NIL                  // result: .F. 


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