NAME

Role::Hooks - role callbacks

SYNOPSIS

  package Local::Role {
    use Moo::Role;
    use Role::Hooks;
    
    Role::Hooks->after_apply(__PACKAGE__, sub {
      my ($role, $target) = @_;
      print "$role has been applied to $target.\n";
    });
  }
  
  package Local::Class {
    use Moo;
    with "Local::Role";   # prints above message
  }

DESCRIPTION

This module allows a role to run a callback when it is applied to a class or to another role.

Compatibility

It should work with Role::Tiny, Moo::Role, Moose::Role, Mouse::Role, and Role::Basic. Not all class builders work well with all role builders (for example, a Moose class consuming a Mouse role). But when they do work together, Role::Hooks should be able to run the callbacks. (The only combination I've tested is Moo with Moose though.)

Some other role implementations (such as Moos::Role, exact::role, and OX::Role) are just wrappers around one of the supported role builders, so should mostly work.

With Role::Basic, the after_apply hook is called a little earlier than would be ideal; after the role has been fully loaded and its methods have been copied into the target package, but before handling requires, and before patching the DOES method in the target package. If you are using Role::Basic, consider switching to Role::Tiny.

Apart from Role::Tiny/Moo::Role, a hashref of additional arguments (things like "-excludes" and "-alias") can be passed when consuming a role. Although I discourage people from using these in general, if you need access to these arguments in the callback, you can check %Role::Hooks::ARGS.

Methods

before_apply
  Role::Hooks->before_apply($rolename, $callback);

Sets up a callback for a role that will be called before the role is applied to a target package. The callback will be passed two parameters: the role being applied and the target package.

The role being applied may not be the same role as the role the callback was defined in!

  package Local::Role1 {
    use Moo::Role;
    use Role::Hooks;
    Role::Hooks->before_apply(__PACKAGE__, sub {
      my ($role, $target) = @_;
      "$role has been applied to $target.\n";
    });
  }
  
  package Local::Role2 {
    use Moo::Role;
    with "Local::Role1";
  }
  
  package Local::Class1 {
    use Moo::Role;
    with "Local::Role2";
  }

This will print:

  Local::Role1 has been applied to Local::Role2.
  Local::Role2 has been applied to Local::Class1.

If you only care about direct applications of roles (i.e. the first one):

  Role::Hooks->before_apply(__PACKAGE__, sub {
    my ($role, $target) = @_;
    return if $role ne __PACKAGE__;
    "$role has been applied to $target.\n";
  });

If you only care about roles being applied to classes (i.e. the second one):

  Role::Hooks->before_apply(__PACKAGE__, sub {
    my ($role, $target) = @_;
    return if Role::Hooks->is_role($target);
    "$role has been applied to $target.\n";
  });
after_apply
  Role::Hooks->after_apply($rolename, $callback);

The same as before_apply, but called later in the role application process.

Note that when the callback is called, even though it's after the role has been applied to the target, it doesn't mean the target has finished being built. For example, there might be has statements after the with statement, and those will not have been evaluated yet.

If you want to throw an error when someone applies your role to an inappropriate target, it is probably better to do that in before_apply if you can.

is_role

Will return true if the given package seems to be a role, false otherwise.

(In fact, returns a string representing which role builder the role seems to be using -- "Role::Tiny", "Moose::Role", "Mouse::Role", or "Role::Basic"; roles built using Moo::Role are detected as "Role::Tiny".)

ENVIRONMENT

The environment variable PERL_ROLE_HOOKS_DEBUG may be set to true to enable debugging messages.

BUGS

Please report any bugs to http://rt.cpan.org/Dist/Display.html?Queue=Role-Hooks.

SEE ALSO

Role::Tiny, Moose::Role.

AUTHOR

Toby Inkster <tobyink@cpan.org>.

COPYRIGHT AND LICENCE

This software is copyright (c) 2020 by Toby Inkster.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

DISCLAIMER OF WARRANTIES

THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.