VecDeque should support splice / extend_front

[Boscop]

VecDeque should support splice for convenience.
(SliceDeque supports it, but it doesn't build on wasm and seems kind of abandoned (several unmerged PRs with no updates).)

VecDeque should also support extend_front (like repeated push_front from an iterator. Compared to calling q.splice(..0, iter), the elements added with q.extend_front(iter) would be in reverse order).

[cynecx]

I had to switch over to using a Vec because I couldn't efficiently insert multiple items into a VecDeque. Having a splice method would've been really useful. If I can find some time these days, I might be able to work on a PR.

[tomkarw]

@rustbot claim

[Boscop]

@tomkarw Thanks for working on this. Btw, what's the current status? :)

[tomkarw]

Sorry for the late response, apparently I don't get GitHub notification via email.

TBH, I thought it will be easier. The unsafe code needed kinda scared me, and I got a job 4 days after claiming this.
I'll try to revisit it now, but will probably look for a mentor/guidance.

[drwilco]

And what about a .prepend() to mirror .append()?

[qvignaud]

Hi, I just found out I'm encountering a case where prepend() and/or extend_front() methods on VecDeque could be really useful.
I'm doing the work by iterating over other vector and push_front repeatedly, but that feels not idiomatic and I guess not optimal at all.

If no one is available for this I might take a look at some point.

[jnb]

+1 for implementing this. Repeatedly calling push_front has a significant performance impact for my use-case, so I ended-up hacking something together on top of a Vec.

[nhtyy]

I wonder what the blockers are here? I might give implementing prepend a shot this weekend.

[tomkarw]

No blockers, just lack of time. Feel free to pick it up, I'll be happy to see it implemented.