In a template class, how to define a property alias conditionally to the template?
Example:
template<class Type, unsigned int Dimensions>
class SpaceVector
{
public:
std::array<Type, Dimensions> value;
Type &x = value[0]; // only if Dimensions >0
Type &y = value[1]; // only if Dimensions >1
Type &z = value[2]; // only if Dimensions >2
};
Is this conditional declaration possible? if yes, how?
Specialise the first two cases:
template<class Type>
class SpaceVector<Type, 1>
{
public:
std::array<Type, 1> value; // Perhaps no need for the array
Type &x = value[0];
};
template<class Type>
class SpaceVector<Type, 2>
{
public:
std::array<Type, 2> value;
Type &x = value[0];
Type &y = value[1];
};
If you have a common base class then you gain a measured amount of polymorphism for common functionality.
static_assert in the primary template to ensure that Dimensions is valid.
If you can do without the array, you could do this:
template<class Type, std::size_t Dimension>
class SpaceVector
{
public:
Type x;
};
template<class Type>
class SpaceVector<Type, 2> : public SpaceVector<Type,1>
{
public:
Type y;
};
template<class Type>
class SpaceVector<Type, 3> : public SpaceVector<Type,2>
{
public:
Type z;
};
This is more scalable if you decide to support more than three elements, but otherwise, Bathsheba's answer is probably more suitable.
