Why should I prefer static constexpr int in a class over enum for class-level integral constants?

Question

C++17 Update: static constexpr variables are implicitly inline so there\'s no external definition necessary.

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Original qu

Answer 1

Perhaps no advantage for your usage because you're just using simple fixed integer values.

But, [AFAIK] constexpr can be more general as it allows initialization from anything that can be evaluated at compile time.

From type_traits:

 /// integral_constant
  template
    struct integral_constant
    {
      static constexpr _Tp                  value = __v;
      typedef _Tp                           value_type;
      typedef integral_constant<_Tp, __v>   type;
      constexpr operator value_type() const { return value; }
#if __cplusplus > 201103L
#define __cpp_lib_integral_constant_callable 201304
      constexpr value_type operator()() const { return value; }
#endif
    };

Thus, constexpr has usage in metaprogramming.

The following is a bit rough.

If you had a function like:

constexpr unsigned
bitmask(int bitno)
{

    return 1u << bitno;
}

You might find a usage such as:

constexpr unsigned BIT_0 = bitmask(0);
constexpr unsigned BIT_1 = bitmask(1);