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MooseX::Method::Signatures(3) User Contributed Perl Documentation MooseX::Method::Signatures(3)

MooseX::Method::Signatures - (DEPRECATED) Method declarations with type constraints and no source filter

version 0.49

    package Foo;
    use Moose;
    use MooseX::Method::Signatures;
    method morning (Str $name) {
        $self->say("Good morning ${name}!");
    method hello (Str :$who, Int :$age where { $_ > 0 }) {
        $self->say("Hello ${who}, I am ${age} years old!");
    method greet (Str $name, Bool :$excited = 0) {
        if ($excited) {
            $self->say("GREETINGS ${name}!");
        else {
            $self->say("Hi ${name}!");
    $foo->morning('Resi');                          # This works.
    $foo->hello(who => 'world', age => 42);         # This too.
    $foo->greet('Resi', excited => 1);              # And this as well.
    $foo->hello(who => 'world', age => 'fortytwo'); # This doesn't.
    $foo->hello(who => 'world', age => -23);        # This neither.
    $foo->morning;                                  # Won't work.
    $foo->greet;                                    # Will fail.

Provides a proper method keyword, like "sub" but specifically for making methods and validating their arguments against Moose type constraints.

Warning: MooseX::Method::Signatures and MooseX::Declare are based on Devel::Declare, a giant bag of crack originally implemented by mst with the goal of upsetting the perl core developers so much by its very existence that they implemented proper keyword handling in the core.
As of perl5 version 14, this goal has been achieved, and modules such as Devel::CallParser, Function::Parameters, and Keyword::Simple provide mechanisms to mangle perl syntax that don't require hallucinogenic drugs to interpret the error messages they produce.
If you want to use declarative syntax in new code, please for the love of kittens get yourself a recent perl and look at Moops and core signatures instead.

The signature syntax is heavily based on Perl 6. However not the full Perl 6 signature syntax is supported yet and some of it never will be.

    method foo (             $affe) # no type checking
    method bar (Animal       $affe) # $affe->isa('Animal')
    method baz (Animal|Human $affe) # $affe->isa('Animal') || $affe->isa('Human')

    method foo ( $a,  $b,  $c) # positional
    method bar (:$a, :$b, :$c) # named
    method baz ( $a,  $b, :$c) # combined

    method foo ($a , $b!, :$c!, :$d!) # required
    method bar ($a?, $b?, :$c , :$d?) # optional

    method foo ($a = 42) # defaults to 42

    method foo ($foo where { $_ % 2 == 0 }) # only even

    method foo (        $moo) # invocant is called $self and is required
    method bar ($self:  $moo) # same, but explicit
    method baz ($class: $moo) # invocant is called $class

    method foo (:     $affe ) # called as $obj->foo(affe => $value)
    method bar (:apan($affe)) # called as $obj->foo(apan => $value)

    method foo (Affe $bar does trait)
    method foo (Affe $bar is trait)
The only currently supported trait is "coerce", which will attempt to coerce the value provided if it doesn't satisfy the requirements of the type constraint.

    method foo ($bar, $, $baz)
Sometimes you don't care about some parameters you're being called with. Just put the bare sigil instead of a full variable name into the signature to avoid an extra lexical variable to be created.

    method foo ( SomeClass $thing where { $_->can('stuff') }:
                 Str  $bar  = "apan",
                 Int :$baz! = 42 where { $_ % 2 == 0 } where { $_ > 10 } )
    # the invocant is called $thing, must be an instance of SomeClass and
           has to implement a 'stuff' method
    # $bar is positional, required, must be a string and defaults to "apan"
    # $baz is named, required, must be an integer, defaults to 42 and needs
    #      to be even and greater than 10

This module is as stable now, but this is not to say that it is entirely bug free. If you notice any odd behaviour (messages not being as good as they could for example) then please raise a bug.

Parse::Method::Signatures is used to parse the signatures. However, some signatures that can be parsed by it aren't supported by this module (yet).

While this module does rely on the hairy black magic of Devel::Declare it does not depend on a source filter. As such, it doesn't try to parse and rewrite your source code and there should be no weird side effects.
Devel::Declare only effects compilation. After that, it's a normal subroutine. As such, for all that hairy magic, this module is surprisingly stable.

Devel::Declare cannot yet change the way "sub" behaves. However, the signatures module can. Right now it only provides very basic signatures, but it's extendable enough that plugging MooseX::Method::Signatures signatures into that should be quite possible.

Type constraints for return values can be declared using
  method foo (Int $x, Str $y) returns (Bool) { ... }
however, this feature only works with scalar return values and is still considered to be experimental.

Methods not seen by a role's "requires"
Because the processing of the MooseX::Method::Signatures "method" and the Moose "with" keywords are both done at runtime, it can happen that a role will require a method before it is declared (which will cause Moose to complain very loudly and abort the program).
For example, the following will not work:
    # in file
    package Canine;
    use Moose;
    use MooseX::Method::Signatures;
    with 'Watchdog';
    method bark { print "Woof!\n"; }
    # in file
    package Watchdog;
    use Moose::Role;
    requires 'bark';  # will assert! evaluated before 'method' is processed
    sub warn_intruder {
        my $self = shift;
        my $intruder = shift;
        $self->bark until $intruder->gone;
A workaround for this problem is to use "with" only after the methods have been defined. To take our previous example, Canine could be reworked thus:
    package Canine;
    use Moose;
    use MooseX::Method::Signatures;
    method bark { print "Woof!\n"; }
    with 'Watchdog';
A better solution is to use MooseX::Declare instead of plain MooseX::Method::Signatures. It defers application of roles until the end of the class definition. With it, our example would becomes:
    # in file
    use MooseX::Declare;
    class Canine with Watchdog {
        method bark { print "Woof!\n"; }
    # in file
    use MooseX::Declare;
    role Watchdog {
        requires 'bark';
        method warn_intruder ( $intruder ) {
            $self->bark until $intruder->gone;
Subroutine redefined warnings
When composing a Moose::Role into a class that uses MooseX::Method::Signatures, you may get a "Subroutine redefined" warning. This happens when both the role and the class define a method/subroutine of the same name. (The way roles work, the one defined in the class takes precedence.) To eliminate this warning, make sure that your "with" declaration happens after any method/subroutine declarations that may have the same name as a method/subroutine within a role.


Bugs may be submitted through the RT bug tracker <> (or <>).
There is also a mailing list available for users of this distribution, at <>.
There is also an irc channel available for users of this distribution, at irc://
I am also usually active on irc, as 'ether' at "".

Florian Ragwitz <>

Karen Etheridge <>
Ash Berlin <>
Daniel Ruoso <>
Justin Hunter <>
Nicholas Perez <>
Dagfinn Ilmari Mannsaaker <>
Rhesa Rozendaal <>
Yanick Champoux <>
Cory Watson <>
Kent Fredric <>
Lukas Mai <>
Matt Kraai <>
Jonathan Scott Duff <>
Jesse Luehrs <>
Hakim Cassimally <>
Dave Rolsky <>
Ricardo SIGNES <>
Sebastian Willert <>
Steffen Schwigon <>

This software is copyright (c) 2008 by Florian Ragwitz.
This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.
2015-10-07 perl v5.28.1

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