The following code example is taken from the book
C++20 - The Complete Guide
by Nicolai M. Josuttis,
Leanpub, 2021
The code is licensed under a
Creative Commons Attribution 4.0 International License.
// raw code
#include "isconsteval.hpp"
#include <iostream>
int main()
{
constexpr int l1 = len("hello"); // uses then branch
int l2 = len("hello"); // uses else branch (no required compile-time context)
std::cout << "l1: " << l1 << '\n';
std::cout << "l2: " << l2 << '\n';
}