Hi.

In a recent proposal vector will gain range construction and append operations. This will allow safely expressing operations that would otherwise require unchecked_emplace_back.

For example a reserve + push_back loop can be replaced by an append with a sized input range. The vector can internally reserve once based on the size, then it can do the equivalent of unchecked_emplace_back in a loop.

Cheers,
Lénárd




-------- Original Message --------
From: Victor Khomenko via Std-Discussion <std-discussion_at_[hidden]>
Sent: October 11, 2021 2:19:59 PM GMT+01:00
To: "std-discussion_at_[hidden]" <std-discussion_at_[hidden]>
Cc: Victor Khomenko <victor.khomenko_at_[hidden]>, Alex <orangechicken_at_[hidden]>
Subject: Re: [std-discussion] Thoughts on making unchecked_emplace_back a public function for vector?

[It's best to use std-proposals list as you're trying to propose a new feature (this list is mostly about the current standard, things like wording/defects).]

I tried to propose something similar back in 2013, see the discussion here:
https://groups.google.com/a/isocpp.org/g/std-proposals/c/5BnNHEr07QM/m/rFgbMSAibioJ

In the course of the discussion, push_back_ was (sensibly) renamed into unchecked_push_back.

My feeling was that people generally disliked this idea, so I didn't get to writing a proposal.

All the best,
Victor.


> -----Original Message-----
> From: Std-Discussion <std-discussion-bounces_at_[hidden]> On Behalf Of
> Alex via Std-Discussion
> Sent: Monday, October 11, 2021 1:53 PM
> To: std-discussion_at_[hidden]
> Cc: Alex <orangechicken_at_[hidden]>
> Subject: [std-discussion] Thoughts on making unchecked_emplace_back a public
> function for vector?
>
> ⚠ External sender. Take care when opening links or attachments. Do not
> provide your login details.
>
> I've been playing around with a slightly modified version of the standard vector
> header for a while now which makes "unchecked_emplace_back" a usable
> function as well as some other utility functions I've added. There's more than a
> few cases I've had so far to use it and net a bit of a bonus bit of performance.
>
> Rough idea is a function (or functions) which assumes a bit more responsibility
> on the side of the user, but it short cuts some redundant checks on the
> containers capacity. In playing around I actually found a different way to go
> about this which was way faster, however I think it might be a stretch because it
> would pretty much allow full access over all the vector's members.
>
> The only thing I'm really wondering is whether this is the right email to send this
> to, some places suggested floating standards proposals here, wasn't exactly
> clear. In any case, thoughts? The edits for reference to existing headers are
> extremely minor, usually because an unchecked version of emplace_back is
> already written as a utility function for emplace_back to work. I also have zero
> reference for whether this has been brought up before.
>
> --
> -Alex Anderson
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