[Bug c++/64232] Derived class with implicitly declared assignment operator is std::is_assignable though base class is not std::is_assignable

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64232

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
std::is_assignable says:

"Only the validity of the immediate context of the assignment expression is
considered. [ Note: The compilation of the expression can result in side
effects such as the instantiation of class template specializations and
function template
specializations, the generation of implicitly-defined functions, and so on.
Such
side effects are not in the “immediate context” and can result in the program
being ill-formed. — end note ]"

i.e. is_assignable isn't magic and can't give the right answer in all cases,
especially if you have members with nonsensical signatures.