MooseX::Method - (DEPRECATED) Method declaration with type checking


  package Foo;

  use MooseX::Method; # Or use MooseX::Method qw/:compiled/

  method hello => named (
    who => { isa => 'Str',required => 1 },
    age => { isa => 'Int',required => 1 },
  ) => sub {
    my ($self,$args) = @_;

    print "Hello $args->{who}, I am $args->{age} years old!\n";

  method morning => positional (
    { isa => 'Str',required => 1 },
  ) => sub {
    my ($self,$name) = @_;

    print "Good morning $name!\n";

  method greet => combined (
    { isa => 'Str' },
    excited => { isa => 'Bool',default => 0 },
  ) => sub {
    my ($self,$name,$args) = @_;

    if ($args->{excited}) {
      print "GREETINGS $name!\n";
    } else {
      print "Hi $name!\n";

  no MooseX::Method; # Remove the MooseX::Method keywords.

  Foo->hello (who => 'world',age => 42); # This works.

  Foo->morning ('Jens'); # This too.

  Foo->greet ('Jens',excited => 1); # And this as well.

  Foo->hello (who => 'world',age => 'fortytwo'); # This doesn't.

  Foo->morning; # This neither.

  Foo->greet; # Won't work.


This module has been deprecated in favor of MooseX::Method::Signatures. It is being maintained purely for people who need more time to change their implementations. It should not be used for new code.


The problem

This module is an attempt to solve a problem I've often encountered but never really found any good solution for: validation of method parameters. How many times have we all ourselves writing code like this:

  sub foo {
    my ($self,$args) = @_;

    die "Invalid arg1"
      unless (defined $arg->{bar} && $arg->{bar} =~ m/bar/);

Manual parameter validation is a tedious, repetive process and maintaining it consistently throughout your code can be downright hard sometimes. Modules like Params::Validate makes the job a bit easier, but it doesn't do much for elegance and it still requires more weird code than what should, strictly speaking, be neccesary.

The solution

MooseX::Method to the rescue! It lets you declare which parameters people should pass to your method using Moose-style declaration and Moose types. It doesn't get much Moosier than this.


  method $name => sub {};

  method $name => named () => sub {};

The exported function method installs a method into the class which call it. The first parameter it takes is the name of the method. The rest of the parameters need not be in any particular order, though it's probably best for the sake of readability to keep the subroutine at the end.

There are two different elements you need to be aware of: the signature and the parameter. A signature is (for the purpose of this document) a collection of parameters. A parameter is a collection of requirements that an individual argument needs to satisfy. No matter what kind of signature you use, these properties are declared the same way, although specific properties may behave differently depending on the particular signature type.

As of version 0.31, signatures are optional in method declarations. If one is not provided, arguments will be passed directly to the coderef.


MooseX::Method ships with three different signature types. Once the internal API stabilizes, you'll be able to implement your own signatures easily.

The three different signatures types are shown below:

  named (
    foo => { isa => 'Int',required => 1 },
    bar => { isa => 'Int' },

  # And methods declared are called like...

  $foo->mymethod (foo => 1,bar => 2);

  positional (
    { isa => 'Int',required => 1 },
    { isa => 'Int' },

  $foo->mymethod (1,2);

  combined (
    { isa => 'Int' },
    foo => { isa => 'Int' },

  $foo->mymethod (1,foo => 2);

The named signature type will let you specify names for the individual parameters. The example above declares two parameters, foo and bar, where foo is mandatory. Read more about parameter properties below.

The positional signature type lets you, surprisingly, declare positional unnamed parameters. If a parameter has the 'required' property set in a positional signature, a parameter is counted as provided if the argument list is equal or larger to its position. One thing about this is that it leads to a situation where a parameter is implicitly required if a later parameter is explicitly required. Even so, you should always mark all required parameters explicitly.

The combined signature type combines the two signature types above. You may declare both named and positional parameters. Parameters do not need to come in any particular order (although positional parameters must be ordered correctly relative to each other like with the positional signature) so it's possible to declare a combined signature like this:

  combined (
    { isa => 'Int' },
    foo => { isa => 'Int' },
    { isa => 'Int' },
    bar => { isa => 'Int' },

This is however not recommended for the sake of readability. Put positional arguments first, then named arguments last, which is the same order combined signature methods receive them. Also be aware that all positional parameters are always required in a combined signature. Named parameters may be both optional or required however.


Currently, a parameter may set any of the following fields:


If a value is provided, it must satisfy the constraints of the type specified in this field. This field should accept the same values as its counterpart in Moose attributes, see the Moose documentation for more details on what you can use.


Require that the value provided is able to do a certain role. It's implied that the value must also be blessed, although setting this property does not alter the isa property.


Sets the parameter to a default value if the user does not provide it.


If this field is set, supplying a value to the method isn't optional but the value may be supplied by the default field.


If the type supports coercion, attempt to coerce the value provided if it does not satisfy the requirements of isa. See Moose for examples of how to coerce.


This is used as parameter metaclass if specified. If you don't know what this means, read the documentation for Moose.


To set a method attribute, use the following syntax:

  method foo => attr (
    attribute => $value,
  ) => sub {};

You can set the default method attributes for a class by using the function default_attr like this:

  default_attr (attribute => $value);

  method foo => attr (
    overridden_attribute => $value,
  ) => sub {};

If you discover any attributes other than those listed here while diving through the code, they're not guaranteed to be in the next release.


Sets the metaclass to use when creating the method.



The function for declaring methods.


A function for constructing a named signature.


A function for constructing a positional signature.


A function for constructing a combined signature.


An alias for the combined structure. Will be removed post version 1.0.


A function for declaring method attributes.


A function for setting the default attributes on methods of a class.


Inside Moose roles, MooseX::Method can be used as sugar for declaring a required method. This is done by not attaching a coderef to method declaration, like this...

  method foo => ();

Which will make MooseX::Method add the method to the list of required methods instead of making it a real method in the role. Signatures in such declarations are at the moment not used, but I'm working with stevan on making it possible to require a specific signature.


As of 0.40, MooseX::Method has experimental support for compiling the signatures into Perl code and inlining it to achieve a significant performance improvement. This behaviour is not enabled by default since it is not yet tested extensively, and may or may not be severely bugged -- but if you dare, you can enable inline compilation with

  use MooseX::Method qw/:compiled/;

And all methods within this class will take adventage of the new experimental feature. This does not affect classes that do not explicitly enable it; the effect is local. If you try this and get an error using it, please make a small test case and send it to me.


I'm considering using a param() function to declare individual parameters, but I feel this might have too high a risk of clashing with existing functions of other modules. Your thoughts on the subject are welcome.


Methods are added to the class at runtime, which obviously means they won't be available to play with at compile-time. Moose won't mind this but a few other modules probably will. A workaround for this that sometimes works is to encapsulate the method declarations in a BEGIN block.

There's also a problem related to how roles are loaded in Moose. Since both MooseX::Method methods and Moose roles are loaded at runtime, any methods a role requires in some way must be declared before the 'with' statement. This affects things like 'before' and 'after'.


Stevan Little for making Moose and luring me into the world of metafoo.
Max Kanat-Alexander for testing.
Christopher Nehren for documentation review.


The #moose channel on


Most software has bugs. This module probably isn't an exception. If you find a bug please either email me, or add the bug to cpan-RT.


Anders Nor Berle <>


Copyright 2007 by Anders Nor Berle.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.