https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80841
--- Comment #4 from Jason Bell <cipherjason at hotmail dot com> --- (In reply to Daniel Krügler from comment #3) > (In reply to Jason Bell from comment #2) > > Thanks that's a good reduced example. I've changed it slightly so it works > > with constexpr input. > > But that is just adding additional complexity: The constexpr declaration is > unnecessary when you provide an argument of reference type to a non-type > template of reference type. I agree that should be the case but with my GCC compiler (6.3.1) on C++14 mode I get an error from that... "error: the value of ‘input’ is not usable in a constant expression" even though it's used as a reference. If I static cast it this problem goes away, but then I get different behaviour on Clang with C++14... So the constexpr version seems a bit more portable for testing this particular issue.
