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[SR-1482] Compare arrays of optionals #44091

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swift-ci opened this issue May 11, 2016 · 6 comments
Closed

[SR-1482] Compare arrays of optionals #44091

swift-ci opened this issue May 11, 2016 · 6 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. standard library Area: Standard library umbrella

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@swift-ci
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Previous ID SR-1482
Radar None
Original Reporter svanimpe (JIRA User)
Type Bug
Status Resolved
Resolution Done
Environment

Xcode 7.3.1

Additional Detail from JIRA
Votes 0
Component/s Standard Library
Labels Bug
Assignee None
Priority Medium

md5: 8eb536899e9dcfae3cd643696fb4a68c

relates to:

  • SR-1535 No == overload exists for comparing optional arrays.
  • SR-2062 Optionals do not conform to CustomStringConvertible
  • SR-1997 Tuples with optional parameter aren't equatable

Issue Description:

The following code is inspired by code I wanted to write for a game of tic-tac-toe:

enum Player { case X, O }
var board: [Player?] = [.X, .X, .X, nil, nil, nil, nil, nil, nil]
let tripleX: [Player?] = [.X, .X, .X]
[0, 1, 2].map { board[$0] } == tripleX

This code does not compile as the operator == does not work for operands of type [Player?]. As a user of Swift, I would expect this to work, as the operator == does work with operands of type Player?.
@belkadan
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This needs a feature called "conditional conformances", so that we know that Optional<T> is Equatable when T is Equatable. There are currently manual overloads for [T] and T?, but not for [T?].

@belkadan
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@gribozavr, would we consider adding such an overload?

@gribozavr
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Given that it will work eventually, I don't see an issue with adding an overload now, as long as there is no fallout (e.g., from implicit conversions that get activated etc.)

Someone needs to champion this API for the evolution process.

@swift-ci
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Comment by David Liu (JIRA)

+1 any word on this?

@gribozavr
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Someone needs to either implement a missing feature in the compiler, or add special-case overloads of == and != to the library. The latter requires a swift-evolution proposal.

@huonw
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huonw mannequin commented Apr 5, 2018

A year and a half later, conditional conformances now exists and Equatable is implemented for optionals and arrays, so this should work!

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. standard library Area: Standard library umbrella
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@belkadan @gribozavr @swift-ci