swiftlang/swift

[SR-3396] `reversed` for sequences and forward collections and should return a `ReversedRandomAccessCollection<[Iterator.Element]>`

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#45,984 opened on 2016年12月12日

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affects ABIgood first issueimprovementstandard libraryswift evolution proposal needed

説明
Previous ID SR-3396
Radar rdar://problem/21098134
Original Reporter @airspeedswift
Type Improvement

Attachment: Download
Votes 0
Component/s Standard Library
Labels Improvement, AffectsABI, StarterProposal
Assignee None
Priority Medium

md5: 34c0ebf025eb58406a81d44f15afed48

Issue Description:

Currently calling reversed() on a bi-directional and random-access collections returns a ReversedCollection and ReversedRandomAccessCollection respectively. This is because the view can be placed over the underlying collection at no cost – it's just a question of transforming the index appropriately and then accessing the underlying base collection.

For sequences and forward-only collections, however, this can't be done. So for these, the contents are read into an array and then that array is in-place reversed. But the second step is unnecessary – the array, once created, could just be returned wrapped in a ReversedRandomAccessCollection. As well as efficiency, this would have the benefit of making these methods more consistent across the board in what they return.

コントリビューターガイド

技術スタック
swift
領域
performance
Issue 種別
performance
難度新しい貢献者にとっての実装難度です。1 は非常に小さな変更、5 は専門的な作業です。
3
推定時間経験ある貢献者が調査、実装、テスト、pull request 準備にかけるおおよその時間範囲です。
half day
活動状況Issue が今どれだけ取り組みやすいかを示します。新しい、活発、古い、ブロック中、またはメンテナー入力待ちなどです。
stale
明確さ期待される変更、受け入れ条件、次の手順がどれだけ明確かを示します。
clear
前提条件
Swift collection protocolsunderstanding of reversed()
初心者向け度初回貢献者にどれだけ取り組みやすいかを 1-100 で推定したスコアです。
75
調査方針
Examine the current implementation of `reversed()` on Sequence and Collection in the Swift standard library (likely in Collection.swift or similar). The goal is to change the return type for sequences and forward only collections to `ReversedRandomAccessCollection` instead of an array. Ensure to handle the case where the sequence is already an array by directly reversing it. Write tests to verify the new behavior and ensure performance improvement. Consult the Swift evolution process for proposals if needed.
[SR-3396] `reversed` for sequences and forward collections and should return a `ReversedRandomAccessCollection<[Iterator.Element]>` · swiftlang/swift#45984 | Good First Issue