//********************************************************
// The following code example is taken from the book
//  C++20 - The Complete Guide
//  by Nicolai M. Josuttis (www.josuttis.com)
//  http://www.cppstd20.com
//
// The code is licensed under a
//  Creative Commons Attribution 4.0 International License
//  http://creativecommons.org/licenses/by/4.0/
//********************************************************


#include <type_traits>
#include <cstring>

constexpr int len(const char* s)
{
  if (std::is_constant_evaluated()) {
    int idx = 0;
    while (s[idx] != '\0') {      // compile-time friendly code 
      ++idx;
    }
    return idx;
  }
  else {
    return std::strlen(s);        // function called at runtime 
  }
}