Why is constexpr with std::forward_as_tuple not working? [duplicate]

问题

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Closed 2 days ago.

Why is the following not compiling? This is somehow counter-intuitive (not to say constexpr concepts are confusing):

#include <tuple>

int main() {
    constexpr const int a   = 0;
    static_assert(a == 0, "Wups");
    constexpr auto t2 = std::forward_as_tuple(a, a);
}

LIVE I assumed that a is a compile-time constant expression which is clearly the case as I can use it in static_assert.

Background: I wanted to continue with constexpr tuple of reference to feed to other constexpr functions to do some compile-time computations

来源：https://stackoverflow.com/questions/59563997/why-is-constexpr-with-stdforward-as-tuple-not-working