On Tue, 22 Sep 2009 21:15:54 -0400, Steven Schveighoffer
<[email protected]> wrote:
BTW, I don't see a huge benefit from your example. If B inherits from
A, then B knows about all the types A knows about (imagining an example
where the parameters were some other class hierarchy, like C and D), so
does it make a lot of sense to limit the arguments to B.fun to a base
class of something B must already know about? I mean, it's not like B
doesn't know about the derived type, how hard would it be to just use
the derived type? Maybe I'm missing something...
OK, here is an abstract example, maybe someone can put some real-world
use-case to it.
I have a base class A which I want to override, but I also want to
implement interface I (assuming I didn't write either of them). They are
defined as follows:
// parameter classes
class X {}
class Y: X {}
class A
{
void foo(Y y) {}
}
interface I
{
void foo(X x);
}
With contravariance, I could do:
class B : A, I
{
void foo(X x) {...}
}
Without contravariance, I don't see how it could be done...
-Steve
