How to move template constructor specialization to cpp file?

Question

I am aware of the reasons why the implementation of templates should go to the header. This question is about template specialization. As far as I understand, this setup should work.

header:

template<class T>
class Foo {

public:
  Foo(T value) {
      // not specialized
  }
};

template<> Foo<double>::Foo(double value);

cpp:

// specialization for float
template<> 
Foo<double>::Foo(double value) {
    // special version for double
}

usage:

Foo<double>(0);

However, i get a compiler error:

error LNK2019: unresolved external symbol "public: __thiscall Foo<double>::Foo<double>(double)" (??0?$Foo@N@@QAE@N@Z) referenced in function _wmain

What am I doing wrong? Is there another way to move specialized constructor to an implementation file?

Answer 1

This looks to me like a bug in the Visual C++ compiler, since the code compiles and links and runs fine with MinGW g++, but I'm not sure.

Anyway, the following workaround header code works with Visual C++.

#pragma once

template<class T>
class Foo
{
public:
    Foo( T )
    {
      // not specialized
    }
};

template<> Foo<double>::Foo( double );
template class Foo<double>;