swiftlang/swift

[SR-1959] Use Bounds.Stride for Index on countable ranges

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#44,568 opened on Jul 1, 2016

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affects ABIgood first issueimprovementstandard libraryswift evolution proposal needed

Description
Previous ID SR-1959
Radar rdar://problem/26302563
Original Reporter @gribozavr
Type Bug
Votes 0
Component/s Standard Library
Labels Bug, AffectsABI, StarterProposal, swift-evolution-proposal-needed
Assignee None
Priority Medium

md5: 6a8b1ccf3e51e9239df2d35454f79393

Issue Description:

CountableRange collection conformance defines an Index type that conforms to Strideable. That is not the case for the CountableClosedRange, which makes the two ranges not interchangeable in all cases.

ClosedRangeIndex implementation uses an internal enum that makes Strideable conformance hard to implement.

The proposed solution is to use Bounds.Stride as Index on both CountableRange and CountableClosedRange.

  • It is proposed to use `Bound.Stride` as index for both countable ranges.

  • The only problem with that is that `SubSequence` of a countable range can no longer be the same type (as indices will not be interchangeable). [Why is this? Someone needs to reconstruct the logic chain.]

  • But it can be solved by using one of the existing slice types for `SubSequence`.

NOTE: Requires a swift-evolution proposal.

Contributor guide

Tech stack
swift
Domain
backenddeveloper experience
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
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.
mostly clear
Prerequisites
SwiftGenericsStrideable protocolABI stability
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
This issue from 2016 proposes using Bound.Stride as the index type for countable ranges to make CountableClosedRange and CountableRange interchangeable. The contributor should first understand the current implementation in the Swift standard library (e.g., Range.swift file) and the challenges with the enum based index for ClosedRangeIndex. Since a swift evolution proposal is required, the first step is to write a pitch for the community and discuss on the forums. After consensus, the implementation can change the index type and adjust the SubSequence type to use existing slice types.