Simple ->DOES override
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    Class::DOES - Provide a simple ->DOES override

        package My::Class;

        use Class::DOES qw/Some::Role/;

        if (My::Class->DOES("Some::Role")) {

    Perl 5.10 introduced a new method in UNIVERSAL: "DOES". This was added
    to support the concept of roles. A role is an interface (a set of
    methods, with associated semantics) that a class or an object can
    implement, without necessarily inheriting from it. A class declares that
    it implements a given role by overriding the "->DOES" method to return
    true when passed the name of the role.

    This is all well and flexible, allowing advanced object systems like
    Moose to implement the "->DOES" override as they see fit, but what about
    ordinary classes that just want to declare they support a known
    interface? That's what this module is for: you pass it a list of roles
    on the "use" line, and it gives you a "->DOES" override that returns
    true for

    - any role in the supplied list;
    - any class you inherit from;
    - any role supported by any class you inherit from.

    It makes the following assumptions:

    - All your inheritance happens through @ISA.
        That is, you haven't overridden "->isa".

    - Noone else has given you a "->DOES" method.
        That is, none of your superclasses have their own "->DOES" override
        (other than one provided by this module).

    If it detects either of these at "use" time, it will issue a warning.

  Setting %DOES directly.
    This module stores the roles you support in the %DOES hash in your
    package. If you want "->DOES" to return something other that 1 for a
    role you support, you can make an entry in your %DOES hash yourself and
    it will be picked up.

    You should not make entries with false values, as this would be very
    confusing. If you do, then when "->DOES" is called it will return 1
    instead of the given value, and will issue a warning.

    All of these can be disabled with

        no warnings "Class::DOES";

    %s has inherited an incompatible ->DOES
        You have issued "use Class::DOES" from a class that already has a
        "->DOES" method. This inherited method will be completely ignored,
        so any roles it claims to support will be lost.

    %s doesn't use @ISA for inheritance
        You have issued "use Class::DOES" from a class with an overriden
        "->isa". Since the exported "->DOES" method uses @ISA to determine
        inheritance, any extra classes "->isa" claims to inherit from will
        not be checked for the requested role.

    $%s::DOES{%s} is false, returning 1
        "->DOES" has found a false entry in a %DOES hash, and is returning 1
        instead to indicate the role is supported.

    Copyright 2009 Ben Morrow <>.

    This program is licensed under the same terms as Perl.

    Please send bug reports to <>.