Dispatch::Class - dispatch on the type (class) of an argument
use Dispatch::Class qw( class_case dispatch ); # analyze the class of an object my $analyze = class_case( 'Some::Class' => 1, 'Other::Class' => 2, 'UNIVERSAL' => "???", ); my $foo = $analyze->(Other::Class->new); # 2 my $bar = $analyze->(IO::Handle->new); # "???" my $baz = $analyze->(["not an object"]); # undef # build a dispatcher my $dispatch = dispatch( 'Dog::Tiny' => sub { ... }, # handle objects of the class Dog::Tiny 'Dog' => sub { ... }, 'Mammal' => sub { ... }, 'Tree' => sub { ... }, 'ARRAY' => sub { ... }, # handle array refs ':str' => sub { ... }, # handle non-reference strings '*' => sub { ... }, # handle any value ); # call the appropriate handler, passing $obj as an argument my $result = $dispatch->($obj);
This module offers a (mostly) simple way to check the class of an object and handle specific cases specially.
The following functions are available and can be imported on request:
class_case
class_case takes a list of KEY, VALUE pairs and returns a code reference that (when called on an object) will analyze the object's class according to the rules described below and return the corresponding VALUE of the first matching KEY.
KEY, VALUE
Example:
my $subref = class_case( KEY1 => VALUE1, KEY2 => VALUE2, ... ); my $value = $subref->($some_object);
This will check the class of $some_object against KEY1, KEY2, ... in order and return the corresponding VALUEn of the first match. If no key matches, an empty list/undef is returned in list/scalar context, respectively.
$some_object
KEY1
KEY2
VALUEn
The following things can be used as keys:
*
This will match any value. No actual check is performed.
:str
This special key will match any non-reference.
SCALAR
ARRAY
HASH
These values match references of the specified type even if they aren't objects (i.e. not blessed). That is, for unblessed references the string returned by ref is compared with eq.
bless
ref
eq
Any other string is interpreted as a class name and matches if the input value is an object for which $obj->isa($CLASS) is true. To match any kind of object (blessed value), use the key 'UNIVERSAL'.
$obj->isa($CLASS)
'UNIVERSAL'
Starting with Perl 5.10.0 Perl supports checking for roles with DOES, so Dispatch::Class actually uses $obj->DOES($CLASS) instead of isa. This still returns true for normal base classes but it also accepts roles that have been composed into the object's class.
DOES
Dispatch::Class
$obj->DOES($CLASS)
isa
dispatch
This works like class_case above, but the VALUEs must be code references and get invoked automatically:
sub dispatch { my $analyze = class_case @_; sub { my ($obj) = @_; my $handler = $analyze->($obj) or return; $handler->($obj) } }
That is, the matching object is passed on to the matched VALUEs and the return value of the inner sub is whatever the handler returns (or the empty list/undef if no KEY matches).
This module uses Exporter::Tiny, so you can rename the imported functions at use time.
Exporter::Tiny
use
Lukas Mai, <l.mai at web.de>
<l.mai at web.de>
Copyright 2013, 2014 Lukas Mai.
This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.
See http://dev.perl.org/licenses/ for more information.
To install Dispatch::Class, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Dispatch::Class
CPAN shell
perl -MCPAN -e shell install Dispatch::Class
For more information on module installation, please visit the detailed CPAN module installation guide.