On Sun, Aug 14, 2005 at 08:28:33PM +0800, Autrijus Tang wrote:
: S06 made many explicit uses of generics as classes, which I find
: difficult to reconcile with the "only roles takes type parameter"
: ruling. For example:
:
: my Hash of Array of Recipe %book;
: my Hash[returns=>Array[returns=>Recipe]] %book;
:
: And later:
:
: class LoudArray is Array { ... }
:
: Clearly, here Hash and Array are used as instantiable, generic classes,
: instead of mere roles. Does this need to change, or can we lift the
: ban on type-parameterized classes?
I think the distinction is still useful to document that there are
still unbound types. What we need to emphasize is that a role can be
used as a class, at which point any unbound types are bound to Any,
or whatever we're calling it these days. I'd say Array is a role,
not a class. So these all might do different things:
class LoudArray is Array { ... }
role LoudArray does Array { ... }
role LoudArray is Array { ... }
Interestingly, what is bound by trait as a container type can still be
a role rather than a class, since the actual class might not be instantiated
till we know the shape, and that might not be known till the time of
elaboration of the variable declaration:
my num @array is shape($x,$y);
That's assuming we treat shapes as a type signature... It doesn't have to
be for integer indexes, maybe, but for hashes:
my Fight %hash is shape(Dog,Cat);
it looks susupiciously like a type signature. Maybe it should be written:
my Fight %hash :(Dog,Cat);
or even
my %hash :(Dog,Cat --> Fight);
Larry
