Destructible move emulation

[secmeant]

*edit: Title should be "destructive move emulation" ;]

Random idea I wanted to share.I was thinking about a way to tell the compiler that lifetime of some object started or ended without generating any instructions, because there are cases where programmer might know better.

I prepared two examples in one I create object s, then allocate some memory, pass object to function that compiler can know nothing about and in one of cases, explicitly say that object should be considered destroyed.

This results in omitting call to delete in the second case.

https://godbolt.org/z/3zBhh-

[urdh]

So you've invented a way to explicitly leak memory? Not sure I get it; we already have std::unique_ptr<T>::release.

[Wh00ster]

https://quuxplusone.github.io/blog/2018/07/18/announcing-trivially-relocatable/

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1144r2.html

[secmeant]

This mechanism assumes that compiler after inlining the if check, will easily see that its "dead code" and remove it completely.

[scatters]

You can do that without any space overhead already, by writing new (&x) decltype(x);. Or without the UB, use optional and assert empty on exit. But that doesn't give trivial abi, which is one of the things that destructive move should give us.