Checking at compile time if specified value is in a range of a type

Question

Is it possible to check this:

template
struct X{};

What I mean by this is, is it possible to check that va

Answer 1

I would say that the direct solution to this question might be this:

   template< typename T, T X, T L, T H>
      using inside_t = 
        std::enable_if_t< (X <= H) && (X >= L), 
           std::integral_constant >;

Applied to the OP:

    template    struct X; // final {};

template
struct X final 
{
    using ascii_ordinal = inside_t;
    char value = char(ascii_ordinal::value);
};

Which renders really terrible CL error messages when it does the job:

X a; //here 300 is out of range and I would like to be able to detect that.

While much less snazzy but most comfortable API might be:

template
struct X final 
{
    static_assert( K >= 0U && K <= 127U, "\n\nTeribly sorry, but value must be between 0 and 127 inclusive\n\n") ;
    char value = char(K);
};