[llvm-bugs] [Bug 43732] static constexpr member is not a constant expression when read from a reference

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43732

Richard Smith <richard-llvm at metafoo.co.uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |INVALID

--- Comment #1 from Richard Smith <richard-llvm at metafoo.co.uk> ---
Clang is correct to reject this; GCC and MSVC are not precisely following the
C++ standard's rules here. The expression 'ref.value' mentions 'ref', which
implicitly reads from the reference; this is not permitted in a constant
expression because the reference does not have a constant initializer.


See:

http://eel.is/c++draft/expr.const#4.12 [you can only mention 'ref' if it is
usable in constant expressions]
http://eel.is/c++draft/expr.const#3.sentence-1 ['ref' is only usable in
constant expressions if it is constant-initialized]
http://eel.is/c++draft/expr.const#2.2 ['ref' is only constant-initialized if
its initializer is a constant expression]
http://eel.is/c++draft/expr.const#10 [the initializer is only a constant
expression if 'a' is a permitted result of a constant evaluation]
http://eel.is/c++draft/expr.const#10.sentence-2 ['a' is not a permitted result
of a constant evaluation because it does not have static storage duration]

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