Dan Sugalski wrote:
We can't devolve to isa checking under the hood, because there are cases where a class can assert that it has a role without pulling in the role externally. (Storable, for example, will be a likely thing here as classes assert they do Storable without pulling in an external Storable role, since a generic Storable's generically useless) So there will be classes that have a role in them without having a class of the same name in their inheritance hierarchy anywhere.
Does, though, can only check the assertions of whether a class does the role in question--it can't check inheritance, because while Perl 6 makes roles and classes more or less the same (kinda sorta) that's not true of other languages. If I have an Objective-C or Java object of class Foo, and Foo implements the Bar interface, then that object does(Bar) while not being isa(Bar), and isa(Foo) without does(Foo).
I'm not sure that this is correct. In Java if you write the following code
class Foo implements Bar
{
}then Foo.new instanceof Bar == true
Ruby's mixins behave similarly.
Actually Ruby uses inheritance to implement mixins. running the following code
module TestMod end
class TestClass include TestMod end
creates an anomynous class that contains a reference to TestMod. This is used as the superclass of TestClass
p TestClass.ancestors #=> [TestClass, TestMod, Object, Kernel]
-- Mark Sparshatt
