Marco Von Ballmoos wrote:
On Apr 5, 2008, at 23:25, Aristotle Pagaltzis wrote:
* Marco Von Ballmoos <[email protected]> [2008-04-05 00:10]:
C#'s generics are better, but still forbid covariance
Have to, to ensure type safety.
It's a matter of opinion whether
the absolute safety from such a slim possibility is worth the reduction
of expressiveness.
My Java is quite rusty, but aren't Java methods supposed to declare
their exceptions, and wouldn't a theoretical possibility of a
ClassCastException thus be a problem with generic methods?
I would
argue that more people would intuitively think that IList<B> inherits
from IList<A> if B inherits from A than that it does not (and that
generic methods are instead required).
I think that the only reasonable test for "is Y a subclass of X?" is
"can I substitute Y objects whenever X objects are used?".
Y="collections of derived class objects" fails this test when
X="collections of base class objects".
Now, lots of actual OO users never use the substitutability test, hence
the Rectangle classes derived from Triangle and vice versa. Should a
language designer care about the intuition of these people?
