Il 13/03/25 16:21, Ell via Std-Discussion ha scritto:
> AFAIUI, if a type is replaceable, then it's possible to, er, replace
> move assignment with destruction + reconstruction. So if std::shared_ptr
> is replaceable, it should be possible to rewrite the previous code as:
>
> template <class T>
> void replace (T& dest, T&& src) {
> dest.~T ();
> new (std::addressof (dest)) T (std::forward<T> (src));
> }

You're right: the semantic requirements for replaceability need to be
more nuanced, and also require that there's no aliasing going on, and
that both objects are owned by the caller of `replace`; or something
along these lines.

Concretely speaking, this requirement was introduced to allow
erasure/insertion in the middle of a std::vector to use (trivial)
relocation instead of assignment. In such a scenario both the extra
properties I described above hold.

My 2 c,
--
Giuseppe D'Angelo