On Thu, Nov 5, 2020 at 11:06 connor horman <chorma...@gmail.com> wrote:
> Looking at https://eel.is/c++draft/optional.optional and optional.assign, > it shouldn't be ill-formed to have a non copy-constructible type, the copy > constructor of optional should be defined as deleted. > [optional.optional.general] clause 3 "T shall be a type other than cv > in_place_t or cv nullopt_t that meets the Cpp17Destructible requirements" > [optional.assign] clause 7 "This operator is defined as deleted unless > is_copy_constructible_v<T> is true and is_copy_assignable_v<T> is true" > > I presume it's the same or similar in both C++17 and C++20 (published) > (with Cpp17Destructible being just Destructible in C++17). > > > On Thu, Nov 5, 2020 at 10:07 Pavel Černohorský via cfe-users < > cfe-users@lists.llvm.org> wrote: > >> On 05. 11. 20 15:47, Marshall Clow via cfe-users wrote: >> >> I tried this code on compiler explorer. >> It compiles w/o error with clang + libc++ >> It fails to compile with clang and libstdc++ >> >> The error message given is: >> >> In file included from <source>:1: >> /opt/compiler-explorer/gcc-10.2.0/lib/gcc/x86_64-linux-gnu/10.2.0/../../../../include/c++/10.2.0/optional:158:7: >> error: the parameter for this explicitly-defaulted copy assignment operator >> is const, but a member or base requires it to be non-const >> operator=(const _Optional_payload_base&) = default; >> ^ >> /opt/compiler-explorer/gcc-10.2.0/lib/gcc/x86_64-linux-gnu/10.2.0/../../../../include/c++/10.2.0/optional:357:7: >> note: in instantiation of template class 'std::_Optional_payload_base<S>' >> requested here >> : _Optional_payload_base<_Tp> >> ^ >> /opt/compiler-explorer/gcc-10.2.0/lib/gcc/x86_64-linux-gnu/10.2.0/../../../../include/c++/10.2.0/optional:631:30: >> note: in instantiation of template class 'std::_Optional_payload<S, true, >> false, false>' requested here >> _Optional_payload<_Tp> _M_payload; >> ^ >> /opt/compiler-explorer/gcc-10.2.0/lib/gcc/x86_64-linux-gnu/10.2.0/../../../../include/c++/10.2.0/optional:660:15: >> note: in instantiation of template class 'std::_Optional_base<S, true, >> true>' requested here >> : private _Optional_base<_Tp>, >> ^ >> <source>:10:20: note: in instantiation of template class >> 'std::optional<S>' requested here >> std::optional<S> a; >> ^ >> 1 error generated. >> >> I got exactly the same error, but the question is why. Shouldn't both g++ >> and clang++ behave the same way even on the libstdc++ (which is the default >> library clang uses on a lot of distros)? Is this gcc being too permissive >> to some bug in libstdc++ or is it a clang bug? Should I file a bug report >> to clang? >> _______________________________________________ >> cfe-users mailing list >> cfe-users@lists.llvm.org >> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users >> >
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