Refer to own type for a template template parameter

Question

Here's the simplest case of what I'm trying to do:

template <template <typename...> class Wrapper>
struct WrapperTraits { };

template <typename... Whatever>
struct Foo {
private:
    // I want Foo here to refer to the template, and not the current
    // concrete type (which is injected into the namespace by default)
    using Traits = WrapperTraits<Foo>;
};

int main()
{
    return 0;
}

And here's the error on clang 3.6 (it compiles fine on gcc 4.8 and 5.2):

error: template argument for template template parameter must be a class template or type alias template
using Traits = WrapperTraits<Foo>;
^
1 error generated.
Compilation failed

Here is the example in question on godbolt: https://goo.gl/cSx6QR

Thanks for your help!

@tobi303 That's on gcc 5.1. It fails to compile on clang. I provided a link on godbolt — Alexander Kondratskiy, Dec 03 '15 at 20:05
Known clang bug. Another workaround is writing `Foo::template Foo`. — T.C., Dec 03 '15 at 20:42

score 2 · Answer 1 · answered Dec 03 '15 at 20:04

Nevermind, figured it out. Need to scope it to the namespace it's in:

template <template <typename...> class Wrapper>
struct WrapperTraits { };


template <typename... Whatever>
struct Foo {
private:
    using Traits = WrapperTraits<::Foo>; // explicit namespace
};


int main()
{
    return 0;
}

Refer to own type for a template template parameter

1 Answers1