Method::Signatures::Simple - Basic method declarations with signatures, without source filters


version 1.07


    # -- a basic class -- #
    package User;
    use Method::Signatures::Simple;

    method new ($class: $name, $email) {
        my $user = {
            id    => new_id(42),
            name  => $name,
            email => $email,
        bless $user, $class;

    func new_id ($seed) {
        state $id = $seed;

    method name  { $self->{name};  }
    method email { $self->{email}; }

    # -- other features -- #
    # attributes
    method foo : lvalue { $self->{foo} }

    # change invocant name
    use Method::Signatures::Simple invocant => '$this';
    method foo ($bar) { $this->bar($bar) }
    method bar ($class: $bar) { $class->baz($bar) }

    # use a different function keyword
    use Method::Signatures::Simple function_keyword => 'fun';
    fun triple ($num) { 3 * $num }

    # use a different method keyword
    use Method::Signatures::Simple method_keyword => 'action';
    action foo { $self->bar }


This module provides basic method and func keywords with simple signatures. It's intentionally simple, and is supposed to be a stepping stone for its bigger brothers MooseX::Method::Signatures and Method::Signatures. It only has a small benefit over regular subs, so if you want more features, look at those modules. But if you're looking for a small amount of syntactic sugar, this might just be enough.


  • invocant

    The method keyword automatically injects the annoying my $self = shift; for you. You can rename the invocant with the first argument, followed by a colon:

        method ($this:) {}
        method ($this: $that) {}

    The func keyword doesn't inject an invocant, but does do the signature processing below:

        func ($that) {}
  • signature

    The signature ($sig) is transformed into "my ($sig) = \@_;". That way, we mimic perl's usual argument handling.

        method foo ($bar, $baz, %opts) {
        func xyzzy ($plugh, @zorkmid) {
        # becomes
        sub foo {
            my $self = shift;
            my ($bar, $baz, %opts) = @_;
        sub xyzzy {
            my ($plugh, @zorkmid) = @_;


Since this module subclasses Devel::Declare::MethodInstaller::Simple, you can change the keywords and the default invocant with import arguments. These changes affect the current scope.

  • change the invocant name

        use Method::Signatures::Simple invocant => '$this';
        method x { $this->{x} }
        method y { $this->{y} }
        # and this of course still works:
        method z ($self:) { $self->{z} }
  • change the keywords

    You can install a different keyword (instead of the default 'method' and 'func'), by passing names to the use line:

        use Method::Signatures::Simple method_keyword   => 'action',
                                       function_keyword => 'thing';
        action foo ($some, $args) { ... }
        thing bar ($whatever) { ... }

    One benefit of this is that you can use this module together with e.g. MooseX::Declare:

        # untested
        use MooseX::Declare;
        class Foo {
            use Method::Signatures::Simple method_keyword => 'routine';
            method x (Int $x) { ... }    # from MooseX::Method::Signatures
            routine y ($y) { ... }       # from this module

    If you specify neither method_keyword nor function_keyword, then we default to injecting method and func. If you only specify one of these options, then we only inject that one keyword into your scope.


        # injects 'method' and 'func'
        use Method::Signatures::Simple;
        # only injects 'action'
        use Method::Signatures::Simple method_keyword => 'action';
        # only injects 'procedure'
        use Method::Signatures::Simple function_keyword => 'procedure';
        # injects 'action' and 'function'
        use Method::Signatures::Simple method_keyword   => 'action',
                                       function_keyword => 'function';
  • install several keywords

    You're not limited to a single use line, so you can install several keywords with the same semantics as 'method' into the current scope:

        use Method::Signatures::Simple; # provides 'method' and 'func'
        use Method::Signatures::Simple method_keyword => 'action';
        method x { ... }
        func y { ... }
        action z { ... }


Rhesa Rozendaal, <rhesa at>


Please report any bugs or feature requests to bug-method-signatures-simple at, or through the web interface at I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.


You can find documentation for this module with the perldoc command.

    perldoc Method::Signatures::Simple

You can also look for information at:



    For writing Devel::Declare and providing the core concepts.


    For writing Method::Signatures and publishing about it. This is what got my attention.


    For helping me abstracting the Devel::Declare bits and suggesting improvements.


    For suggesting we add a 'func' keyword.


Devel::Declare, Method::Signatures, MooseX::Method::Signatures.


Copyright 2011 Rhesa Rozendaal, all rights reserved.

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