On 12/11/2021 04.04, Hani Deek via Std-Discussion wrote:
> The following code is accepted by GCC, Clang and MSVC. I thought it was ill-formed because the variable V0 is not usable in constant expressions. Is this just a bug in all of those compilers? Or is there an explanation in the C++ rules?
>
> struct S{ constexpr operator int() const{ return 0; } };
>
> void foo(S V0) { constexpr int V1 = V0; }
>
> int main()
> {
>    S V0{}; 
>    foo(V0);
> }

There is no lvalue-to-rvalue conversion on any part of V0.

Do you feel any other provision in [expr.const] p5 should
apply, making this not a constant expression?

Jens