Question

I’m using the following pattern to keep template declarations and implementations separate:

---

decl.h (declaration)

template <typename T>
struct Foo
{
  void DoIt();
}

---

impl.cpp (implementation)

template <typename T>
void Foo<T>::DoIt() { // impl code 
};

template class Foo<int>;
template class Foo<float>;

---

Now i want to add a new method to Foo, but the impl.cpp file is already huge, so i want to move it to a separate file impl2.cpp;

---

decl.h (declaration)

template <typename T>
struct Foo
{
  void DoIt();
  void RemoveIt();
}

---

impl.cpp (implementation)

template <typename T>
void Foo<T>::DoIt() { // impl code 
};

template class Foo<int>;
template class Foo<float>;

---

impl2.cpp (implementation)

template <typename T>
void Foo<T>::RemoveIt() { // impl code 
};

template class Foo<int>;
template class Foo<float>;

---

the main concern here are the duplicate instantiations, how do i avoid those?

Answer 1

Do as follows:

1. Move definition of Foo<T>::DoIt() to some header file named
   ImplDoIt.h (not necessarily in the same directory as decl.h)
2. Same for Foo<T>::RemoveIt() – ImplRemoveIt.h
3. Include in your impl.cpp all these header files and instantiate the templates.