Question

If the title isn’t clear, the code should help clarify:

// .h file    
template<class T> class DF_Vector3
{
public:

    T x, y, z;

    static const DF_Vector3 ZERO;

    DF_Vector3() {}
    DF_Vector3( T F );
    DF_Vector3( T X, T Y, T Z );
};

typedef DF_Vector3<DF_FLOAT> DF_Vector3F;

// .cpp file
template<> const DF_Vector3F DF_Vector3F::ZERO( 0.0f, 0.0f, 0.0f ); // ERROR: Explicit specialization of 'ZERO' after instantiation

The compiler subsequently cites another location where DF_Vector3F::ZERO is referenced and states: “Implicit instantiation first required here.”

The Visual Studio 2010 compiler doesn’t seem to mind this. However, Apple’s CLANG (LLVM) compiler does not like it (it’s the one complaining).

Is there a way to fix this? Thanks.

Answer 1

You cannot use the typedef in the definition of the static members, because by the time you have a typedef, the class template is already instantiated, after which you cannot explicity specialized its member(s).

You should do this:

//general case
template<class T> 
const DF_Vector3<T> DF_Vector3<T>::ZERO;

//specialization
template<> 
const DF_Vector3<DF_FLOAT> DF_Vector3<DF_FLOAT>::ZERO(0.0f, 0.0f, 0.0f);

//after that define the typedef
typedef DF_Vector3<DF_FLOAT> DF_Vector3F; //after

Demo : http://ideone.com/AMWMC