By: mathw

mathw — Thu, 30 Sep 2010 07:38:28 +0000

What you’re doing there is actually creating a new class on the fly which has the role composed into it (and contains nothing else), and then making a new object of that class immediately. I don’t think it’s the kind of thing you can then seamlessly merge into an instance of another class which composes the same role.

Which I suspect is why the .perl comes out wrong, although it should probably manage to be smarter than that.

But I think the correct pattern here might be having a Duration object which then becomes a member of the thing which has a duration. I did once come across a genuine use for roles, but I was coding in C++ so I had to use multiple inheritance instead. I know people are using them with Moose, but personally I have no idea of the patterns involved.

By: Benabik

Benabik — Thu, 30 Sep 2010 03:42:33 +0000

According to S12…

role Duration {…}
my $x = Duration.new

…is the same as…

role Duration {…}
class Duration does Duration {…}
my $x = Duration.new

I quote from S12-objects.pod:

When the typename happens to be a role, autovivifying it involves
attempting to create a punned class of the same name as the role.
Whether this succeeds or not depends on whether the role is
sufficiently complete to serve as a class on its own.

Comments on: Durations vs Roles

By: mathw

By: Benabik