swiftlang/swift

[SR-10858] Bridging NSString-keyed Dictionaries should only set allowsDuplicates if there are non-ASCII (non-NFC?) Strings

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#53,248 opened on Jun 7, 2019

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Dictionarygood first issueimprovementstandard library

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Description
Previous ID SR-10858
Radar None
Original Reporter @Catfish-Man
Type Improvement
Status In Progress
Resolution
Votes 1
Component/s Standard Library
Labels Improvement, StarterBug
Assignee valeriyvan (JIRA)
Priority Medium

md5: d18df56f9579713f39cb8ff948cf30ca

Issue Description:

Currently we have code like this:

// String and NSString have different concepts of equality, so
// string-keyed NSDictionaries may generate key collisions when bridged
// over to Swift. See rdar://problem/35995647
let handleDuplicates = (Key.self == String.self)
      
result = Dictionary(_unsafeUninitializedCapacity: numElems,
   allowingDuplicates: handleDuplicates) { keys, vals in

This is overly conservative. We only actually need to set allowingDuplicates if there are non-NFC NSStrings!

Contributor guide

Research direction
Locate the dictionary bridging code in the Swift standard library that handles NSString keys, and determine how to conditionally set allowsDuplicates only when non NFC NSStrings are present.
Tech stack
swift
Domain
backend
Issue type
Performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
1
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
SwiftFoundation
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
85