There are times that you want to use a role, but only as an interface.
If 9 out of 10 classes use the implementation, it's annoying to have
that 10th class have to do this:
with 'My::Role' => { excludes => \...@a_long_list_of_methods };
What about something like this?
with 'My::Role' => { includes => [] };
That
would be the mutually exclusive opposite of 'excludes'. No methods
would be composed into your class, but they would all be added to the
'requires' list. This (I think) would largely overcome chromatic's
objection (http://use.perl.org/comments.pl?sid=42835&cid=68295)
that if someone wants to use a role as an interface, being forced to
manually exclude every method is annoying and would discourage role
use. So a role could be trivially used as an interface, if desired,
even if implementation is provided.
Plus, if you still needed two of the 8 methods a role provided:
with 'My::Role' => { includes => [qw{ foo bar }] };
Seems to me that this is the best of both worlds. This would also make it
trivial to add the "warn on conflict" back in because the entire objection
seemed to be that the warning coupled with it being annoying to exclude all
methods would discourage role use (an argument which penalizes the programmer
who values safety and correctness, but then, Dominus doesn't like how we
constantly encourage "use strict", either). While I do realize I've lost this
argument, at least adding "includes" would make roles a tad more flexible and
make some of my work easier if I get around to writing "MooseX::Role::Strict".
This
also shows what I *think* is a limitation in 'excludes'. All methods
listed in a role should be explicitly added to the 'requires' list.
The following is a runtime failure:
#!/usr/bin/env perl
package My::Role;
use Moose::Role;
sub foo { __PACKAGE__ }
package Bar;
use Moose;
with 'My::Role' => { excludes => 'foo' };
print Bar->foo;
# Can't locate object method "foo" via package "Bar" at role.pl line 13.
Thoughts?
Cheers,
Ovid
--
Buy the book - http://www.oreilly.com/catalog/perlhks/
Tech blog - http://use.perl.org/~Ovid/journal/
Twitter - http://twitter.com/OvidPerl
Official Perl 6 Wiki - http://www.perlfoundation.org/perl6
