"Nicholls, Mark" <[EMAIL PROTECTED]> wrote:
> [snip]
Extension methods don't do inference that can't be done by normal method
call inference either - the fact that the error occurs with extension
methods is irrelevant. Calling an extension method M defined in class C
using the extension syntax x.M() is equivalent to trying to call it as
C.M(x), and the equivalent transformation in your problem case has the
same failure.
The problem isn't so much the dependency in the generic constraints, but
rather that the generic type arguments can't be inferred using the
actual argument types. Your Extension.Test method is parameterized over
two types, but only uses one of those types in the argument list, so the
inference can't be completed - it's like having two variables but only
one equation. The generic constraints aren't used in the inference
process.
I've rewritten your case to expose why it can't be solved in general,
too; I also changed the definition of Test<,> to distinguish between B<>
the generic type and B the type argument.
Here's a different version which would have ambiguous resolutions if the
generic constraints were actually used in the inference process:
---8<---
using System;
static class Program
{
static void Main()
{
C t = new C();
t.Test(); // #1
t.Test<int,C>(); // #2
t.Test<string,C>(); // #3
}
}
public interface B<T>
{
}
public class C : B<int>, B<string>
{
}
public static class Extension
{
static public void Test<T,U>(this U self)
where U : B<T>
{
}
}
--->8---
As you can see here, there are two possible inferences (in this case)
for T, #2 and #3.
-- Barry
--
http://barrkel.blogspot.com/
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