GCC moved it to <optional> with the release of GCC7. Note that we're now at GCC8, clang 4 added it - I believe we're now at clang 6. Therefore, it's by far no

GCC moved it to <optional> with the release of GCC7. Note that we're now at GCC8, clang 4 added it - I believe we're now at clang 6. Therefore, it's by far no longer something that's experimental IMHO. (standardised in C++17 after all)