How to detect if a func. Is a constexpr? And mark other func. Constexpr depending on it?

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Assuming i have some function template f1:

C++

template<typename f2>
int f1(int i, int j) throw() {
  return i + j + f2(i, j);
}

is there way to determine if 'f2(i, j)' can be a constexpr. (no matter it is a func. or a functor) and so mark 'f1' as a constexpr. too?

What I have tried:

I am thinking of using SFINAE here some how, but didn't find how to detect constexpr. using type traits.

Posted 23-Jun-16 2:56am

Shvetsov Evgeniy

Updated 2-Jul-16 8:20am

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[no name] 3-Jul-16 9:17am

Why do you want to do this. Are you trying to force f1 to be computed at compile time if f2 is a constexpr. What assumptions are you making?

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KarstenK · Answer 1 · 2016-07-02T08:20:00

Solution 1

As Is understand the constexpr it is a compile time qualifier, so you MUST declare f2 also as constexpr.

C++

template <constexpr typename="" f2="">
constexpr int f1(int i, int j) throw() {
  return i + j + f2(i, j);
}</constexpr>

Posted 2-Jul-16 8:20am

KarstenK