lst-0047-book.cpp
// https://godbolt.org/z/v3x7nGs3f
int get_input() {
return 50; // or read something from a file or so
}
constexpr auto calculate_1(int input) {
return input * 2;
}
consteval auto calculate_2(int input) {
return input * 2;
}
int main() {
int input = get_input();
auto a = calculate_1(77); // at compile time … maybe computable
auto b = calculate_1(input); // … computable, but valid
auto c = calculate_2(77); // … computable
auto d = calculate_2(input); // (ERR) … not computable, invalid
}