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.
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).
-doy
