NAME

MooseX::Method - Method declaration with type checking

SYNOPSIS

  package Foo;

  use MooseX::Method;

  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";
    }
  };

  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.

DESCRIPTION

The problem

This module is an attempt to solve a problem I've often encountered but never really found any good solution for, namely validation of method parameters. How many times haven't we all found 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 and 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 what parameters people should be passing to your method using Moose-style declaration and Moose types. It doesn't get much Moosier than this.

DECLARING METHODS

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

The exported function method installs a method into the class from which it is called from. The first parameter it takes is the name of the method. The rest of the parameters needs 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 of this module, signatures are optional in method declarations. If one is not provided, arguments will be passed directly to the coderef.

Signatures

MooseX::Method comes with three different signature types, and you will once the internal API becomes stable 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, of which foo is mandatory. Read more about parameter properties below.

The positional signature type lets you, unsurprisingly, 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 right 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 in. Be also aware that all positional parameters are always required in a combined signature. Named parameters may be both optional or required however.

Note: "combined" used to be known as "semi". You can still use "semi" to declare combined signatures, but this will probably stop working sometimes after version 1.0 is released.

Parameters

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

isa

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.

does

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.

default

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

required

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

coerce

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.

metaclass

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

Attributes

To set a method attribute, use the following syntax:

  method foo => attr (
    attribute => $value,
  ) => named (
    # Regular parameter stuff here
  ) => sub {};

You can set the default method attributes for a class by having a hashref with them returned from the method _default_method_attributes like this:

  sub _default_method_attributes { attr (attribute => $value) }

  method foo => attr (
    overridden_attribute => $value,
  ) => named (
    # Regular parameter stuff here
  ) => sub {};

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

metaclass

Sets the metaclass to use for when creating the method.

FUTURE

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

CAVEATS

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 work 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 runtime, any methods a role requires in some way must be declared before the 'with' statement. This affects things like 'before' and 'after'.

ACKNOWLEDGEMENTS

Stevan Little for making Moose and luring me into the world of metafoo.

SEE ALSO

Moose

The #moose channel on irc.perl.org

BUGS

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.

AUTHOR

Anders Nor Berle <debolaz@gmail.com>

COPYRIGHT AND LICENSE

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.

cpanm MooseX::Method

perl -MCPAN -e shell
install MooseX::Method