this post was submitted on 25 Nov 2023
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On harmful overuse of std::move - The Old New Thing (devblogs.microsoft.com)
submitted 10 months ago by [email protected] to c/[email protected]
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[–] [email protected] 1 points 9 months ago (2 children)

I wonder if the language could be updated so these extra std::move invocations actually become harmless? return std::move is something that I see used quite a bit.

These std::move invocations are harmless, as they only cast objects to their rvalue reference.

The destructive bit takes place in the type they are assigned to, as it invokes either a move constructor or a move assignment operator, and calling those implies that the object you just passed to std::move will be invalidated after the call and should not be used subsequently.

[–] [email protected] 1 points 9 months ago (1 children)

@lysdexic @QuadriLiteral Eh, no. Really. Changing the value category disables RVO

[–] [email protected] 1 points 9 months ago (1 children)

RVO

I recommend you read the thread.

[–] [email protected] 1 points 9 months ago (1 children)

@lysdexic I did.

[–] [email protected] 1 points 9 months ago (1 children)

It doesn't look like it, otherwise you'd be aware that the whole point of this submission is that casting return values with std::move disables RVO.

[–] [email protected] 1 points 9 months ago (1 children)

@lysdexic You claimed otherwise:
"
These std::move invocations are harmless, as they only cast objects to their rvalue reference.
"
If you were right, we wouldn't have the motivation to look at this in EWG.

[–] [email protected] 1 points 9 months ago

If you were right, we wouldn’t have the motivation to look at this in EWG.

I am right. Not benefiting from RVO does not mean you're harming anyone.

Again, I recommend you read the submission and also the discussion.

[–] [email protected] 1 points 9 months ago

I mean harmless in a way that using std::move on the return type doesn't prevent RVO?