On 28 March 2013 17:45, Jesse Luehrs <d...@tozt.net> wrote:
> On Thu, Mar 28, 2013 at 05:42:18PM +0000, Piers Cawley wrote:
>> On 28 March 2013 17:36, Piers Cawley <pdcaw...@bofh.org.uk> wrote:
>> > On 28 March 2013 16:41, Jesse Luehrs <d...@tozt.net> wrote:
>> >> On Thu, Mar 28, 2013 at 09:20:55AM -0700, Ovid wrote:
>> >>> Ouch! You're right. My apologies for the confusion. The examples should
>> >>> be this:
>> >>>
>> >>> use 5.01000;
>> >>> { package a; use Moose::Role; sub result { 'a' } }
>> >>> { package b; use Moose::Role; }
>> >>> { package c; use Moose::Role; with qw(a b); sub result { 'c' } }
>> >>> { package d; use Moose::Role; with qw(c); }
>> >>> {
>> >>> package Consumer; use Moose;
>> >>> with 'd';
>> >>> }
>> >>> say Consumer->new->result;
>> >>>
>> >>> Versus:
>> >>>
>> >>> use 5.01000;
>> >>> { package a; use Moose::Role; with qw(b c); sub result { 'a' } }
>> >>> { package b; use Moose::Role; }
>> >>> { package c; use Moose::Role; sub result { 'c' } }
>> >>> { package d; use Moose::Role; with qw(a); }
>> >>> {
>> >>> package Consumer; use Moose;
>> >>> with 'd';
>> >>> }
>> >>> say Consumer->new->result;
>> >>>
>> >>> Only the order of role consumption is changed, but the behavior is now
>> >>> different.
>> >>
>> >> I can't really agree here that "only the order of role consumption is
>> >> changed". I certainly wouldn't have the expectation that those two code
>> >> snippets would necessarily produce the same result. The reason for this
>> >> change is to bring role composition in roles into line with how role
>> >> composition in classes works. For instance, here:
>> >>
>> >> package a; use Moose::Role; sub result { 'a' }
>> >> package b; use Moose; sub result { 'b' }
>> >>
>> >> This has always worked without error. On the other hand, this:
>> >>
>> >> package a; use Moose::Role; sub result { 'a' }
>> >> package b; use Moose::Role; sub result { 'b' }
>> >>
>> >> has historically been a conflict error, and one that has bit me (and
>> >> several other people) on several occasions. I have never meant anything
>> >> other than the behavior that happens in the class case, so I don't see
>> >> why extending that behavior to the role case is a problem. (Or is it
>> >> your opinion that the first snippet there should also be a conflict?)
>> >>
>> >> In general, I can't really understand why the behavior for roles and
>> >> classes should be different in this sense. A role consuming another role
>> >> is a different operation from role summation, and one that I think
>> >> should behave more similarly to a class consuming a role. Note that this
>> >> is still a conflict:
>> >>
>> >> { package a; use Moose::Role; sub result { 'a' } }
>> >> { package b; use Moose::Role; }
>> >> { package c; use Moose::Role; sub result { 'c' } }
>> >> { package d; use Moose::Role; with qw(a b c); }
>> >>
>> >> The other benefit here is that with this change, alias and excludes
>> >> become completely unnecessary, and can hopefully be deprecated.
>> >
>> > Whoah! What? So when I want to compose, say a and b and write my own
>> > 'result' which will combine a's result and b's result, what am I
>> > supposed to do?
>> >
>> > I'd always been under the impression that when I do:
>> >
>> > with qw(a b);\
>> >
>> > I'm expressing the expectation that there are no conflicts between
>> > those two roles and I want an (ideally compile time) error if they do
>> > conflict, and I can get in and fix it through judicious use of
>> > excludes (and possibly an alias or two).
>> >
>> > If I want the order of composition to matter, then I can do
>> >
>> > with 'a';
>> > with 'b';
>> >
>> > For the life of me I can't see how this change can be called a good idea.
>> >
>> >> If what you're after here is a way to disallow all forms of silent
>> >> method overriding, I think this is better done in an extension (since it
>> >> would have to catch conflicts in inheritance situations as well anyway).
>> >
>> > That's certainly not what I'm after. But I do want to retain the
>> > difference between 'with qw(a b)' and 'with q(a); with q(b);' thank
>> > you very much.
>> >
>> > Who cooked up this idea?
>>
>> To clarify: I'm all for having this:
>>
>> package a; use Moose::Role; sub result { 'a' };
>> package b; use Moose::Role; with 'a'; sub result { 'b' }
>>
>> work without throwing any warnings, but if that comes at the expense of:
>>
>> package a; use Moose::Role; sub result { 'a' };
>> package b; use Moose::Role; sub result { 'b' };
>> package c; use Moose; with qw(a b);
>
> No, this is still a conflict. Role composition and role summation are
> two separate processes.
Ah. Fair enough. Misunderstanding Ovid's original code sample.
