/ 
Switch-Perlish-1.0.0
River stage one • 1 direct dependent • 1 total dependent
/ Switch::Perlish

NAME

Switch::Perlish - A Perlish implementation of the switch statement

VERSION

1.0.0 - Initial release

SYNOPSIS

use Switch::Perlish;

switch $var, sub {
  case 'foo',
    sub { print "$var is equal to 'foo'\n" };
  case 42,
    sub { print "$var is equal to 42\n";
          fallthrough };
  case [qw/ foo bar baz /],
    sub { print "$var found in list\n" };
  case { foo => 'bar' },
    sub { print "$var key found in hash\n" };
  case \&func,
    sub { print "$var as arg to func() returned true\n" };
  case $obj,
    sub { print "$var is method in $obj and returned true\n" };
  case qr/\bfoo\b/,
    sub { print "$var matched against foo\n" };
  default
    sub { print "$var did not find a match\n" };
};

BACKGROUND

If you're unfamiliar with switch then this is the best place to start. A switch statement is essentially syntactic sugar for an if/elsif/else chain where the same $variable is tested in every conditional e.g:

my $foo = 'a string';
if($foo eq 'something') {
  print '$foo matched "something"';
} elsif($foo eq 'a string') {
  print '$foo matched "a string"';
} else {
  print '$foo matched nothing';
}

This simply matches $foo against a series of strings, then defaulting to the last else block if nothing matched. An equivalent switch statement (using this module) would be:

use Switch::Perlish;
my $foo = 'a string';
switch $foo, sub {
  case 'something',
    sub { print '$foo matched "something"' };
  case 'a string',
    sub { print '$foo matched "a string"'  };
  default
    sub { print '$foo matched nothing' };
};

So the first argument to switch is the thing to be tested (in code above, $foo), and the second argument is the block of tests. Each case statement matches its first argument against $foo, and if the match is successful, the associated block is executed, so running the above code outputs: $foo matched "a string". Note the use of semi-colon at the end of the switch, case and default calls - they're just simple subroutine calls.

DESCRIPTION

This is a Perl-oriented implementation of the switch statement. It uses smart-matching in cases which can be configured and extended by the user. There is no magical syntax so switch/case/default expect coderefs, which are most simply provided by anonymous subroutines. By default successful case statements do not fall through[1]. To get fall through functionality call the fallthrough subroutine explicitly.

[1] To 'fall through' in a case block means that the switch block isn't exited upon success

Smart Matching

The idea behind smart matching is that the given values are matched in an intelligent manner, so as to get a meaningful result regardless of the values' types. This allows for flexible code and a certain amount of "just do it" when using smart matching. Below is a basic example using smart matching (which is done implictly in case) where a simple value is being matched against an array e.g

use Switch::Perlish;

my $num = $ARGV[0];

switch $num, sub {
  case undef,
    sub { die "Usage: $0 NUM\n" };
  case [0 .. 10],
    sub { print "Your number was between 0 and 10" };
  case [11 .. 100],
    sub { print "Your number was between 11 and 100" };
  case [101 .. 1000],
    sub { print "Your number was between 101 and 1000" };
  default
    sub { print "Your number was less than 0 or greater than 1000" };
};

So here the smart matching is checking for the existence of $num in the provided arrays. In the above code ranges happen to be used, but any array would suffice. To see how different value types compare with each other see. Switch::Perlish::Smatch::Comparators, which lists all the default comparators.

The code behind this smart matching can be found in Switch::Perlish::Smatch which itself delegates to the appropriate comparator subroutine depending on the value types. See Switch::Perlish::Smatch for more details on the smart matching implementation and how it can be extended.

SUBROUTINES

switch( $topic, $block );

Execute the given $block allowing case statements to access the $topic.

case( $match, $block );

If $topic smart-matches successfully against $match then execute $block and exit from switch. NB: this cannot be called outside of switch, if you want to use smart matching functionality, see. Switch::Perlish::Smatch.

default( $block )

Execute $block and exit from switch. NB: this cannot be called outside of switch.

fallthrough()

Fall through the the current case block. NB: this cannot be called outside of switch.

Globals

$SWITCH

The current switch block.

$CASE

The current case block.

$TOPIC

The current topic block, also aliased to $_.

$MATCH

The current thing being matched against.

SEE. ALSO

Switch

perlfaq7

Switch::Perlish::Smatch

Switch::Perlish::Smatch::Comparators

TODO

  • Use a version control system

  • Implement localizing comparators

  • Test with earlier versions of perl

AUTHOR

Dan Brook <cpan@broquaint.com>

COPYRIGHT

Copyright (c) 2005, Dan Brook. All Rights Reserved. This module is free software. It may be used, redistributed and/or modified under the same terms as Perl itself.