CPAN::Groonga

package App::InteractivePerlTutorial::Chapter::Smartmatch::Smartmatch;

use 5.014000;
use strict;
use warnings;
our $VERSION = '0.000_001';

use constant TEXT => 'Smart Matching';

1;
__DATA__

=encoding utf-8

=head1 Smart matching

Basically, smart matching(C<~~>) look at both his operators and decides what to do with them.

=head3 Table for smart match operations for pairs of operands

  Example                        Type of match
  -------                        -------------
  %x ~~ %y                       hash keys identical
  %x ~~ @y or @x ~~ %y           at least one key in %x is in @y
  %x ~~ /text/ or /text/ ~~ %y   at least one key matches pattern
  'text' ~~ %x                   exists $x{text}
  @x ~~ @y                       arrays are the same
  @x ~~ /text/                   at least one element in @x matches pattern
  $name ~~ undef                 $name is not defined
  $name ~~ /text/                pattern match
  123 ~~ ’123.0’                 numeric equality with numeric like string
  ’text’ ~~ ’text’               string equality
  123 ~~ 456                     numeric equality

For example:

  if ( 1 ~~ 'zero+1' ) { say 'hi' }
  if ( 'zero+1' ~~ 1 ) { say 'bye' }

will only print 'hi'. This is because in the first case, since the first argument is a number, the ~~ will be the equivalent with the == and will transform the second argument into a number. In the second case, the first argument is a string so the ~~ operator will be equivalent of the eq and so will transform number 1 in string '1'.
~~ is very useful in the cases from the first 6 lines of the list above. For example writing a code which checks if any key from hash %PC matches 'virus' and prints it would take:

  my $corrupt_file = 0;
  foreach my $file ( keys %PC ) {
  next unless $file = /virus/;
  $corrupt_file = $file;
  last;
  }

  if ( $corrupt_file ) { say "WARNING! I found a virus on your PC. It's in $corrupt_file" }

instead of just:

  if( /virus/ ~~ %PC ) { say 'WARNING! I found a virus on your PC.' }


=cut