language: C++11 (gcc-4.7.2)
date: 797 days 8 hours ago
link:
visibility: private 
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#include <iostream>
 
template <int I>
struct Traits
{
  struct inner{};
};
 
template <>
struct Traits<1>
{
  struct inner{
    template<class T1>
    struct impl{
      impl() { std::cout << "impl<T1>" << std::endl; }
    };
  };
};
 
template <>
struct Traits<2>
{
  struct inner{
    template<class T1, class T2>
    struct impl{
      impl() { std::cout << "impl<T1, T2>" << std::endl; }
    };
  };
};
 
template<class T>
struct Test{};
 
template<class T, class K>
struct Foo{};
 
template<int I>
struct arg{};
 
template<
  template<class, class> class T,
  class P1, int I
>
struct Test< T<P1, arg<I> > >{
  typedef typename Traits<I>::inner inner;      
};
 
template<
  template<class, class> class T,
  class P2, int I
>
struct Test< T<arg<I>, P2 > >{
  typedef typename Traits<I>::inner inner;      
};
 
// and a bunch of other partial specializations
 
int main(){
 
  typename Test<Foo<int, arg<1> > >::inner::impl<int> b;
  typename Test<Foo<int, arg<2> > >::inner::impl<int, double> c;
}