class template specialization and inheritance

[Fawzi Mohamed]

On 2008-05-14 00:55:41 +0200, mki <none at none.com> said:

> Hello!
> 
> I just discovered the template syntax of D. I am very exited about its 
> simplicity compared to C++.
> 
> Now I ran into a template behavior I do not understand. This code:
> 
> *** begin code 1 ***
> import std.stdio;
> 
> class A { }
> 
> class B : A { }
> 
> class C(T:A) {
>     static void tellMe() {
>         writefln("derived from A.");
>     }
> }
> 
> class C(T) {
>     static void tellMe() {
>         writefln("generic.");
>     }
> }
> 
> void main() {
>     C!(A).tellMe();
>     C!(B).tellMe();
>     C!(int).tellMe();
> }
> *** end code 1 ***
> 
> as expected produces the output:
> 
> derived from A.
> derived from A.
> generic.
> 
> 
> But this code
> *** begin code 2 ***
> import std.stdio;
> 
> class A(T) { }
> 
> class B(T) : A!(T) { }
> 
> class C(TT:A!(T)) {
>     static void tellMe() {
>         writefln("derived from A!(T).");
>     }
> }
> 
> class C(T) {
>     static void tellMe() {
>         writefln("generic.");
>     }
> }
> 
> void main() {
>     C!(A!(int)).tellMe();
>     C!(B!(int)).tellMe();
>     C!(int).tellMe();
> }
> *** end code 2 ***
> 
> gives the output:
> derived from A!(T).
> generic.
> generic.
> 
> 
> In the second line I would expect the output "derived from A!(T)", like 
> in the example of code 1. My feeling is that for C!(B!(int))
> 'class C(TT:A!(T))'
> with TT=B!(T) and T=int should be a better specialization than
> 'class C(T)'
> with T=B!(T).
> 
> Why is 'class C(T)' chosen here?

It looks like a bug to me, I would write a report on
	http://d.puremagic.com/issues/

maybe you should rewrite the messages to "T is derived from ...", 
because C is not derived from those classes, and the message is 
misleading.

Fawzi