c/cpp · by gracicot@discuss.tchncs.de · 3y

The move constructor that you have to declare, even though you don't want anyone to actually call it - The Old New Thing

https://devblogs.microsoft.com/oldnewthing/20230612-00/?p=108329

9 points · 6 comments · view on lemmy.world

6 Comments

tunetardis@lemmy.ca · 3 pts · 3y (4 replies)

That's fascinating.

NVRO being optional annoys me. I'm always debating whether I should std::move the return value just in case, but if the compiler performs NVRO (which it probably does), this may be a pessimization right? Ugh.

perivesta@feddit.de · 3 pts · 3y (1 reply)

I think you should never std::move return values. Afaik every modern compiler does NRVO and manually moving prevents it. And on the offchance you need to use a compiler that optimizes less, that one copy most likely is the least of the performance concerns.

tunetardis@lemmy.ca · 1 pts · 3y

Afaik every modern compiler does NRVO and manually moving prevents it.

Yeah this is what bothers me. std::move could make things worse, but not if the alternative is a copy. But you're probably right that any self-respecting compiler nowadays would do NRVO.

gracicot@discuss.tchncs.de · 1 pts · 3y (1 reply)

I think compiler move return value by default, so even without NRVO you should never move a return value when it's a local non reference variable.

tunetardis@lemmy.ca · 1 pts · 3y

Well the test3 example FTA gives a case where NRVO would not happen because of the conditional return value. Are you suggesting that you need not std::move even in this case?