How can I enable/disable a function depending on the size of an array?-CodePudding

I'm still rather new to TMP so forgive me if this is a poorly worded question.

I'm trying to make a very generic mathematical Vector class to store any number of components, but defaults to 3 and using float as it's base representation. So if you default construct one of these vectors it will hold (0.0f,0.0f,0.0f)

The values themselves are stored in a std::array and I would like to create accessor function for ease of use. I currently have this:

std::array<Type,SIZE> e;
Type x() const {return e.at(0);};
Type y() const {return e.at(1);};
Type z() const {return e.at(2);};

What I am trying to do now is also have one for the 4th component, w but only enable it if the size of this array is >= 4. so something like this:

template<class Type, std::enable_if<.......>>
Type w() const {return e.at(3);};

This is just a vague idea of what I think it should look like. I'm aware concept exists, but I'm also struggling to write one for this situation.

CodePudding user response：

With concepts you can simply do

Type w() const requires (SIZE >= 4) {return e.at(3);};

CodePudding user response：

Prior to C 20 concepts, you can do this:

template<typename Type = float, size_t SIZE = 3>
class Vector {
    std::array<Type, SIZE> e;
public:
    template<typename Dummy = void, std::enable_if_t<SIZE >= 1, Dummy>* = nullptr>
    Type x() const { return e[0]; };

    template<typename Dummy = void, std::enable_if_t<SIZE >= 2, Dummy>* = nullptr>
    Type y() const { return e[1]; };

    template<typename Dummy = void, std::enable_if_t<SIZE >= 3, Dummy>* = nullptr>
    Type z() const { return e[2]; };

    template<typename Dummy = void, std::enable_if_t<SIZE >= 4, Dummy>* = nullptr>
    Type w() const { return e[3]; };
};

Vector v1;
v1.x();
v1.y();
v1.z();
//v1.w(); // ERROR
    
Vector<int, 4> v2; 
v2.x();
v2.y();
v2.z();
v2.w(); // OK

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