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Re: Questions + bikeshed for reorderase

From: Edward Catmur <ecatmur_at_[hidden]>
Date: Sun, 3 Sep 2023 21:17:30 -0500
This is a pretty vague thought, but have you noticed the correspondence to
the partition / stable_partition algorithms? partition is essentially a way
to accomplish the swap part of a swap-and-pop, and stable_partition is more
or less identical to remove_if, so it feels like maybe there should be an
equivalent using move instead of swap that operates on iterators/ranges
instead of containers, leaving two consecutive ranges where the first part
contains the desired elements and the second is moved-from.

Anyway, great work and thanks.

On Sun, Sep 3, 2023, 18:06 Matt Bentley via SG14 <sg14_at_[hidden]>

> Yeah there's a few issues, such as whether to support deques, but I
> figured one thing at a time. Given lack of response, might be best to
> discuss at next meeting.
> Can't use swap in the name as mentioned - as no swaps occur.
> Cheers for getting back to me.
> On 4/09/2023 10:16 am, Patrice Roy wrote:
> In PXXX, I put « Move-With-Last-Swap / Reorderase » for the moment and
> we'll find a better name if needed (it's a bit early for that). I'd focus
> on the technical issues initially, and feel LEWG's mood for the name.
> Thanks!
> Le jeu. 24 août 2023 à 20:07, Matt Bentley via SG14 <sg14_at_[hidden]>
> a écrit :
>> Hi all-
>> as per the last meeting there was some support for putting forward a
>> proposal for what I call reorderase (plflib.org/reorderase.htm) but is
>> really just an iteration of the swap-and-pop idiom, optimized (no swap,
>> just move) and extended to range-erase and std::erase_if/std::erase. See
>> the page for more information.
>> There was some discussion of this back in 2015 by Brent Freidman but he
>> was focused on the erase_if equivalents - which're the worse-performing of
>> the set.
>> I have a few questions before putting a paper together, the first of
>> which is bikeshedding. I'm pretty settled on the name 'move_pop', for
>> reasons which will become clear, but I am open to suggestions. Please let
>> me know what you think:
>> Names which aren't appropriate:
>> - I like portmanteau's but the standard doesn't, so I'm guessing
>> 'reorderase' is out of the question; possibly unfair on non-english
>> speakers.
>> - Anything with 'swap' in it. Implies operations which do not occur,
>> also implies allocation.
>> - Anything with 'unstable' in it - in the case of the standard
>> library the term 'unstable' is not defined or used, only the term 'stable'
>> is defined. In addition the word has a bad connotation in terms of
>> programs, and algorithms are assumed to be unstable by-default where
>> 'stable' is not used in functions.
>> - Anything long like 'unstable', 'disordered', 'unordered',
>> 'reordering', etc; at least for the singular/range reorderase equivalents.
>> They are expected to be commonly-used functions, so long is Bad. I don't
>> mind a longer title on the erase_if/remove_if equivalent as this is
>> expected to be less-frequently used.
>> - Anything involving 'back' or 'front'. A deque would want to pop
>> from the front if location == begin() or first == begin() (in
>> reorderase(first, last)), and we would want the name to be consistent
>> between deques and vectors/inplace_vectors (if we want to support deques).
>> Potential names:
>> - move_pop/move_and_pop (the standard currently has about 1 other
>> function which uses _and_ but it seems an unnecessary elongation) - this is
>> good enough, and short, and brings in the 'pop' association with being
>> quick/O(1).
>> - ...? Suggestions?
>> - For an std::erase_if/std::erase equivalent, using the 'pop' thing
>> won't work, as erase_if already does this (moves the stuff to the back,
>> erases it). If we go with a remove_if-equivalent implementation instead of
>> erase_if, pop also doesn't work because remove_if doesn't erase/pop
>> anything. I'm leaning towards (assuming a remove_if equivalent member
>> function instead of erase_if) 'unordered_remove_if'/'unordered_remove', or
>> 'disordered_remove_if'/'disordered_remove'. I prefer the latter is it
>> clearly implies that there *will be* a disruption of order in the use
>> of this function.
>> M@
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Received on 2023-09-04 02:17:45