What's the real difference between "constinit" and "constexpr"? [duplicate]

Question

constexpr int f() { return 0; }
int g() { return 0; }

constexpr auto c1 = f(); // OK
constinit auto c2 = f(); // OK

constexpr auto d1 = g(); // ill-formed
constinit auto d2 = g(); // ill-formed

int main() {}

As illustrated in the code above, I cannot find any difference between constinit and constexpr.

What's the real difference between constinit and constexpr?

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Update:

The related What is constinit in C++20? doesn't clearly state the difference between constinit and constexpr.

Frail

@E_net4thedupefinder, the answer in your link doesn't clearly state the difference between constinit and constexpr. – Frail

Yes, it does. The very first answer goes into explicit detail about what constexpr entails and how constinit does not imply most of those things. – Earthlight

Answer 1

A constinit variable is constant initialized, but it is not usable in a constant expression, nor even automatically constant. Your main can legally contain this line

c2 = 2; 

Yup, modification is possible after initialization.

Pallette

From cppreference: "constexpr mandates that the object must have static initialization and constant destruction and makes the object const-qualified, however, constinit does not mandate constant destruction and const-qualification." Just for me, can you just hint me what does this constant destruction means; just how constexpr mandates this and constinit is not. – Teamwork

@AccessDenied - I can't. As far as I can tell this is something that appears only on cppreference, and so may very well be cooked up by whomever edited that entry. – Pallette