some_method_spec.cpp

#include <iostream>
 
template<typename T>
struct Foo
{
    void do_something();
 
    Foo()
    {
        std::cout << "ctor" << std::endl;
    }
};
 
template<>
void Foo<int>::do_something()
{
    std::cout << "int" << std::endl;
}
 
template<>
void Foo<double>::do_something()
{
    std::cout << "double" << std::endl;
}
 
int main()
{
    Foo<int>().do_something();
    Foo<double>().do_something();
    
    return 0;
}

It compiles and works under gcc and MSVS.