swiftlang/swift

[SR-3419] Strides should be collections

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#46,007 opened on Dec 14, 2016

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affects ABIgood first issueimprovementstandard libraryswift evolution proposal needed

Description
Previous ID SR-3419
Radar rdar://problem/17816925
Original Reporter @airspeedswift
Type Improvement
Votes 0
Component/s Standard Library
Labels Improvement, AffectsABI, StarterProposal, swift-evolution-proposal-needed
Assignee None
Priority Medium

md5: 20684cd6a789b38a9426158bdf2d0b60

Issue Description:

In Swift 3.0, StrideTo and StrideThrough conform to Sequence, but not Collection.

While they can't be bi-directional or random-access, as the last (or abitrary) element can't necessarily be reached in O( n ) for all strideable types, it should be possible to make them forward-only collections. One straightforward implementation would be to make the index each value zipped with a count (for Comparable purposes).

Once we have conditional conformance, it should be possible to make specific strides (e.g. ones over integers) conform to random access.

Contributor guide

Tech stack
swift
Domain
api
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Swift protocolsCollection conformanceGenericsSwift standard library
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
Review the current StrideTo and StrideThrough implementations in the Swift standard library to understand their Sequence conformance. Explore how to add Collection conformance by creating a custom index type that pairs each stride value with a count. Investigate the possibility of conditional conformance for random access strides over integer types.
[SR-3419] Strides should be collections · swiftlang/swift#46007 | Good First Issue