Is it possible to determine the number of elements of a c++ enum class?

Question

Is it possible to determine the cardinality of a c++ enum class:

enum class Example { A, B, C, D, E };

I tried to use si

Answer 1

There is one trick based on X()-macros: image, you have the following enum:

enum MyEnum {BOX, RECT};

Reformat it to:

#define MyEnumDef \
    X(BOX), \
    X(RECT)

Then the following code defines enum type:

enum MyEnum
{
#define X(val) val
    MyEnumDef
#undef X
};

And the following code calculates number of enum elements:

template  void null(T...) {}

template 
constexpr size_t countLength(T ... args)
{
    null(args...); //kill warnings
    return sizeof...(args);
}

constexpr size_t enumLength()
{
#define XValue(val) #val
    return countLength(MyEnumDef);
#undef XValue
}

...
std::array some_arr; //enumLength() is compile-time
std::cout << enumLength() << std::endl; //result is: 2
...