> On Nov 5, 2020, at 6:34 AM, Pavel Černohorský via cfe-users
> <cfe-users@lists.llvm.org> wrote:
>
> Hello,
>
> I would like to ask what is wrong with the following code:
> ```
>
> #include <optional>
>
> struct S
> {
> S& operator=(S&) { return *this; };
> };
>
> void thisWillNotCompileInClang()
> {
> std::optional<S> a;
> }
>
> ```
>
> Compilation command is `g++ or clang++ -std=c++17 -c source.cpp`. It compiles
> without problems with g++ 9.3.0, but not with clang++ 10.0.0 (both from
> current stable Ubuntu 20). This code is simplification of code using widely
> adopted rapidjson library which uses assignment operator with non-const
> parameter a lot. Earlier versions of clang did not complain (tried with 7.0.1
> on currently stable Debian Buster).
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.
— Marshall_______________________________________________
cfe-users mailing list
cfe-users@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
