http://d.puremagic.com/issues/show_bug.cgi?id=10183

           Summary: Eponymous template instance fails to match in
                    parameter list of other templates
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: jakobovrum@gmail.com


--- Comment #0 from Jakob Ovrum <jakobovrum@gmail.com> 2013-05-27 03:57:40 PDT ---
Code:
----
struct A(T, Unused)
{
    T t;
}

template B(T)
{
    alias B = A!(T, void);
}

void foo(T)(A!T a) {}

void main()
{
    auto b = B!int(42); // OK, works

    foo(b); // NG - causes error
}
----
Output:
----
test.d(18): Error: template test.foo does not match any function template
declaration. Candidates are:
test.d(12):        test.foo(T)(A!(T) a)
test.d(18): Error: template test.foo(T)(A!(T) a) cannot deduce template
function from argument types !()(A!(int, void))
----

Could be a duplicate, but I don't know what to search for. Does not appear to be a regression.

The call to `foo` works when the second template parameter of A is removed.

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--- Comment #1 from Jakob Ovrum <jakobovrum@gmail.com> 2013-05-27 04:07:18 PDT ---
Thinking more about it, I guess this might not be meant to work.

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Kenji Hara <k.hara.pg@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID


--- Comment #2 from Kenji Hara <k.hara.pg@gmail.com> 2013-05-27 04:58:31 PDT ---
(In reply to comment #0)
> Code:
> ----
> struct A(T, Unused)
> {
>     T t;
> }
> 
> template B(T)
> {
>     alias B = A!(T, void);
> }
> 
> void foo(T)(A!T a) {}

The pattern A!T means that the template A has _exactly_ one type template argument.

> void main()
> {
>     auto b = B!int(42); // OK, works
> 
>     foo(b); // NG - causes error

But the type of b is A!(int, void), so it does not match to A!T during IFTI.

> }

In this case, template function foo should have following signature.

void foo(TL...)(A!TL a) {}
// TL would be deduced to (int, void)

or

void foo(T, TL...)(A!(T, TL) a) {}
// T would be deduced to int
// TL would be deduced to (void)

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--- Comment #3 from Jakob Ovrum <jakobovrum@gmail.com> 2013-05-27 06:04:44 PDT ---
Yeah, I noticed after posting.

The problem with the amended caller code is that it leaks implementation details, as it were. It would be nice if there was a good way to solve this particular abstraction problem.

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