[Bug c++/107202] New: inheriting assignment operators from CRTP-base
h2+bugs at fsfe dot org
gcc-bugzilla@gcc.gnu.org
Mon Oct 10 19:32:00 GMT 2022
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107202
Bug ID: 107202
Summary: inheriting assignment operators from CRTP-base
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: h2+bugs at fsfe dot org
Target Milestone: ---
I stumbled over the following:
```cpp
#define OPTION 0 // or 1-4
template <typename Derived>
struct Base
{
Base() = default;
Base(Base const &) = default;
Base(Base &&) = default;
//Base & operator=(Base const &) = delete;
//Base & operator=(Base &&) = delete;
#if OPTION == 1
Derived const & operator=(Derived &)
{
return static_cast<Derived &>(*this);
}
#elif OPTION == 2
Derived const & operator=(Derived &) const
{
return static_cast<Derived &>(*this);
}
#elif OPTION == 3
Derived const & operator=(Derived const &)
{
return static_cast<Derived &>(*this);
}
#elif OPTION == 4
Derived const & operator=(Derived const &) const
{
return static_cast<Derived &>(*this);
}
#endif
};
struct D : Base<D>
{
D() = default;
D(D const &) = default;
D(D &&) = default;
//D & operator=(D const &) = delete;
//D & operator=(D &&) = delete;
using Base<D>::operator=;
};
int main()
{
D d1;
D d2;
d1 = d2;
}
```
OPTION == 0 → no valid overload (expected!)
OPTION == 1 → well-formed
OPTION == 2 → ambiguous overload
OPTION == 3 → no valid overload
OPTION == 4 → no valid overload
Clang behaves the same as GCC. MSVC never sees any valid overloads.
My assumption was that implicit assignment operators are inhibited in all cases
(this is also shown by OPTION == 0), but that any of the inherited operators
should be valid. Should the implicit deletion of the assignment-operator in D
prevent inheriting the user-defined assignment operators from Base, why does
this affect some of them and not others?
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