marlam - 5 months ago 26

C++ Question

I am just writing on a MathVector class

`template<typename T> MathVector`

{

using value_type = T;

// further implementation

};

However, the class is thought to work with fundamental types but also with a, lets say, Complex class

`template<typename T> Complex`

{

using value_type = T;

// further implementation

};

which offers for example the member functions

`template<typename T> Complex<T>& Complex<T>::operator*=(const Complex<T>& c);`

template<typename T> Complex<T>& Complex<T>::operator*=(const T& c);

Now, for the MathVector class also a multiplication is definded:

`template<typename T> MathVector<T>& MathVector<T>::operator*=(const MathVector<T>& c);`

This is fine for

`T=double`

`T=Complex<double>`

`double`

`Complex<double>`

This is aggravated by the fact that the Code should also work in CUDA device code (I ommited the specifier

`__host__ __device__`

First I thought of an additional template parameter

`template<typename T, typename U> MathVector<T>& MathVector<T>::operator*=(const U& c);`

But this seems dangerous to me, because

`U`

`T`

`T::value_type`

The second idea is to use template specialization

`template<typename T, typename U> MathVector<T>& MathVector<T>::operator*=(const U& c)`

{

static_assert(sizeof(T) == 0, "Error...");

}

template<typename T> MathVector<T>& MathVector<T>::operator*=(const typename T::value_type& c)

{

// implementation

}

But this will not work with fundamental types any more!

I have seen the solutions of this (or a very similar) problem in C++ Operator Overloading for a Matrix Class with Both Real and Complex Matrices and Return double or complex from template function, but they are solved using the standard library in a way which is not possible for CUDA.

So my question is: Is there a way to overload the operator that works with fundamental types and with types that serve a

`value_type`

`std::`

`nvcc`

Answer

You could make `operator*=`

non-member function templates, and provide all the overloads, make SFINAE to take effect.

```
template<typename T>
MathVector<T>& operator*=(MathVector<T>& m, const MathVector<T>& c);
template<typename T>
MathVector<T>& operator*=(MathVector<T>& m, const T& c);
template<typename T>
MathVector<T>& operator*=(MathVector<T>& m, const typename T::value_type& c);
```

Then call them as:

```
MathVector<Complex<double>> m1;
m1 *= MathVector<Complex<double>>{}; // call the 1st one
m1 *= Complex<double>{}; // call the 2nd one
m1 *= 0.0; // call the 3rd one
MathVector<double> m2;
m2 *= MathVector<double>{}; // call the 1st one
m2 *= 0.0; // call the 2nd one
```