NAME

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

SYNOPSIS

On Perl v5.38 or later:

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

   if($str eqr $pat) {
      say "x and y are both undef, or both defined and equal strings, " .
          "or y is a regexp that matches x";
   }

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

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

   match($str : eqr) {
      case(undef)   { say "The variable is not defined" }
      case("")      { say "The variable is defined but is empty" }
      case(qr/^.$/) { say "The variable contains exactly one character" }
      default       { say "The string contains more than one" }
   }

DESCRIPTION

This module provides an infix operators that implements a matching operation whose behaviour depends on whether the right-hand side operand is undef, a quoted regexp object, or some other value. If undef, it is true only if the lefthand operand is also undef. If a quoted regexp object, it behaves like Perl's =~ pattern-matching operator. If neither, it behaves like the eq operator.

This operator does not warn when either or both operands are undef.

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.

Comparison With Smartmatch

At first glance it would appear a little similar to core perl's ill-fated smartmatch operator (~~), but this version is much simpler. It does not try to determine if stringy or numerical match is preferred, nor does it attempt to make sense of any ARRAY, HASH, CODE or other complicated container values on either side. Its behaviour is in effect entirely determined by the value on its righthand side - the three cases of undef, some qr/.../ object, or anything else.

This in particular makes it behave sensibly with the match/case syntax provided by Syntax::Keyword::Match.

OPERATORS

eqr

   my $matches = $lhs eqr $rhs;

Yields true if both operands are undef, or if the right-hand side is a quoted regexp value that matches the left-hand side, or if both are defined and contain equal string values. Yields false if given exactly one undef, two unequal strings, or a string that does not match the pattern.

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_eqr

   my $matches = is_eqr( $lhs, $rhs );

A function version of the "eqr" stringy operator.

SEE ALSO

• Syntax::Operator::Equ - equality operators that distinguish undef

AUTHOR

Paul Evans <leonerd@leonerd.org.uk>