Find out the parameter is constexpr

Question

Any type_traits or method could find out the parameters is a constexpr or not?

Example

size_t fibo_runtime(size_t num)
{
  //implementation
}

constexpr          


        

Answer 1

Within the function, it isn't possible to check the parameters to see if the complete calling expression is a constant expression. But you can implement a macro at the call site to test the same thing, evaluating to true_type or false_type at compile time depending on whether the expression is a constant expression

IS_A_CONSTANT_EXPRESSION(  fibo(5)          )    // is constant
IS_A_CONSTANT_EXPRESSION(  fibo(time(NULL)  )    // is not constant

The details are in this answer to another question. (My own answer, apologies for cross posting!)

You could then implement another macro, FIBO( expr ) to wrap this up nicely and call the correct version as appropriate.