Syntax::Operator::Equ(3pm)

NAME
"Syntax::Operator::Equ" - equality operators that distinguish "undef"

SYNOPSIS
On Perl v5.38 or later:

   use v5.38;
   use Syntax::Operator::Equ;

   if($x equ $y) {
      say "x and y are both undef, or both defined and equal strings";
   }

   if($i === $j) {
      say "i and j are both undef, or both defined and equal numbers";
   }

Or via Syntax::Keyword::Match on Perl v5.14 or later:

   use v5.14;
   use Syntax::Keyword::Match;
   use Syntax::Operator::Equ;

   match($str : equ) {
      case(undef) { say "The variable is not defined" }
      case("")    { say "The variable is defined but is empty" }
      default     { say "The string is non-empty" }
   }

DESCRIPTION
This module provides infix operators that implement equality tests of strings or numbers similar to perl's "eq" and "==" operators, except that they consider "undef" to be a distinct value, separate from the empty string or the number zero.

These operators do not warn when either or both operands are "undef". They yield true if both operands are "undef", false if exactly one operand is, or otherwise behave the same as the regular string or number equality tests if both operands are defined.

Support for custom infix operators was added in the Perl 5.37.x development cycle and is available from development release v5.37.7 onwards, and therefore in Perl v5.38 onwards. The documentation of XS::Parse::Infix describes the situation in more detail.

While Perl versions before this do not support custom infix operators, they can still be used via "XS::Parse::Infix" and hence XS::Parse::Keyword. Custom keywords which attempt to parse operator syntax may be able to use these. One such module is Syntax::Keyword::Match; see the SYNOPSIS example given above.

OPERATORS

  equ
   my $equal = $lhs equ $rhs;

Yields true if both operands are "undef", or if both are defined and contain equal string values. Yields false if given exactly one "undef", or two unequal strings.

  ===
   my $equal = $lhs === $rhs;

Yields true if both operands are "undef", or if both are defined and contain equal numerical values. Yields false if given exactly one "undef", or two unequal numbers.

Note that while this operator will not cause warnings about uninitialized values, it can still warn if given defined stringy values that are not valid as numbers.

FUNCTIONS
As a convenience, the following functions may be imported which implement the same behaviour as the infix operators, though are accessed via regular function call syntax.

These wrapper functions are implemented using XS::Parse::Infix, and thus have an optimising call-checker attached to them. In most cases, code which calls them should not in fact have the full runtime overhead of a function call because the underlying test operator will get inlined into the calling code at compiletime. In effect, code calling these functions should run with the same performance as code using the infix operators directly.

  is_strequ
   my $equal = is_strequ( $lhs, $rhs );

A function version of the "equ" stringy operator.

  is_numequ
   my $equal = is_numequ( $lhs, $rgh );

A function version of the "===" numerical operator.

SEE ALSO

•   Syntax::Operator::Eqr - string equality and regexp match operator

AUTHOR
Paul Evans <leonerd@leonerd.org.uk>