How to implement partial specialized template on void separate from definition?

Question

I have a problem in separating the implementations of an inner class while having partial specializations. Here is a sample code that illustrate my problem:

#include <type_traits>

template <typename T>
using enable_if_copyable = std::enable_if_t<std::is_copy_constructible<T>::value>;

template <typename T>
using enable_if_not_copyable = std::enable_if_t<!std::is_copy_constructible<T>::value>;

template <typename T, typename Enabled=void> 
struct Foo;

template <typename T>
struct Foo<T, enable_if_copyable<T>>
{
    struct Bar
    {
        Bar();
    };
};

template <typename T>
struct Foo<T, enable_if_not_copyable<T>> {
    struct Bar
    {
        Bar();
    };
};

template <>
struct Foo<void,void>
{
    struct Bar
    {
        Bar();
      //Bar() {} This compiles, but it is not what I want.
    };
};

template <typename T>
Foo<T, enable_if_copyable<T>>::Bar::Bar()
{}    

template <typename T>
Foo<T, enable_if_not_copyable<T>>::Bar::Bar()
{}

template <>
Foo<void, void>::Bar::Bar() // this does not compile
{}


int main() {
    Foo<int>::Bar b;
    Foo<void>::Bar v;
}

Because of dependencies I have to implement the c'tors of Bar outside their declaration. My problem is that all compiler (Clang, gcc, Visual Studio 2015) complain about the implementation of Foo<void, void>::Bar::Bar() {} outside of the declaration of class Foo<void, void>. If I implement the c'tor of Bar inside the specialization on void, I don't have any problem. Is this is not doable or is there one who could help me to spot my problem? Many thanks in advance!

Answer 1

Try deleting the template<>; i mean:

// template <>
Foo<void, void>::Bar::Bar() // now compile
{}

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