Can't derive Copy for structs containing arrays

[mahkoh]

Since Copy: Clone and arrays implement Copy but not Clone.

Whose bright idea was it to have a language item depend on an arbitrary trait?

[retep998]

impl Clone for Blah { fn clone(&self) -> Blah { *self } }

[mahkoh]

No shit. Then why doesn't #[derive(Copy, Clone)] do this?

[retep998]

Because #[derive] is unable to inspect what traits are already implemented for a type to choose the appropriate implementation.

[retep998]

However you do bring up a good point with that Copy: Clone yet arrays impl Copy but not Clone. That's definitely something that needs to be fixed, and I believe integer generics are the key to solving it.

[mahkoh]

Because #[derive]is unable to inspect what traits are already implemented for a type to choose the appropriate implementation.

Looks like you found the solution: Change derive to be able to do this.

[lilyball]

@mahkoh You raise a legitimate issue, but you need to watch your language and tone of voice. The way you've written your ticket and replies is unnecessarily rude, and this isn't an isolated incident.

[solson]

@mahkoh Hey, we can solve this problem without being rude about it. This is an annoying wart, for sure, but it's not the end of the world, and it will get fixed.

[mahkoh]

@kballard @tsion Interesting.

[nikomatsakis]

@mahkoh that was implemented as part of PR #23905. I was just encouraging erickt on IRC to extract that out as a separate thing, in fact.

[eternaleye]

@mahkoh #23905 may be of interest.

I will note that your tone comes across as quite confrontational, while the Rust community seems to strive for a more collaborative atmosphere in my experience.

[retep998]

@mahkoh Sorry about all the people that decided to take over this issue to point out your rudeness. (You should still try to be nicer to people in the community though, so people wouldn't have to complain.)

[steveklabnik]

@retep998 that's one reason why rudeness is so bad: it's a distraction from the technical point at hand.

[mahkoh]

@nikomatsakis

Yes, this PR explicitly handles #[derive(Copy, Clone)]

Then that should solve the problem.