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PR libstdc++/77288 * include/std/optional (__is_optional_impl, __is_optional): Remove. (__converts_from_optional, __assigns_from_optional): New. (optional(_Up&&)): Use is_same instead of __is_optional. (optional(const optional<_Up>&)): Constrain with __converts_from_optional. (optional(optional<_Up>&&)): Likewise. (operator=(_Up&&)): Use is_same instead of __is_optional, check is_same and is_scalar. (operator=(const optional<_Up>&)): Constrain with __converts_from_optional and __assigns_from_optional. (operator=(optional<_Up>&&)): Likewise. * testsuite/20_util/optional/77288.cc: New. * testsuite/20_util/optional/cons/value.cc: Adjust. From-SVN: r240324
file: libstdc++-v3/README New users may wish to point their web browsers to the file index.html in the 'doc/html' subdirectory. It contains brief building instructions and notes on how to configure the library in interesting ways.