AW: [std-proposals] Relocation in C++

On Wed, 18 May 2022 at 07:54, Sebastian Wittmeier <wittmeier@projectalpha.org> wrote:

*I would suggest that in those situations - 'reloc a' without using the result - the compiler may just call the destructor and end the scope instead of relocating to a new instance.*

Yes, that sounds a very good idea, however there is something to consider: what happens if `a` cannot be destroyed immediately, if it is a function parameter without trivial or user relocation operation? Since you want to release resources, it will be necessary to move-construct a temporary instance of `T` from `a`, then destroy the temporary. On the other hand, if `T` has trivial or user relocation operation, then even if it is a function parameter the function is in full control of its lifetime so it can be destroyed immediately.

This could possibly be accomplished by an elision rule - eliding relocate + destroy to just relocate. However, that would make it optional and a matter of optimization with user-visible effects. It would probably be better to adjust the rules on *discarded-value expression* such that temporary materialization conversion is not applied if the discarded-value expression is a relocation expression. It would be important to ensure that this has the desired effect of move-constructing and destroying a temporary if necessary.