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.
-doy
