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[SR-7523] flatMap should be compact map in specific case #50065

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swift-ci opened this issue Apr 24, 2018 · 4 comments
Open

[SR-7523] flatMap should be compact map in specific case #50065

swift-ci opened this issue Apr 24, 2018 · 4 comments
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@moiseev
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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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@swift-ci
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Previous ID SR-7523
Radar None
Original Reporter plivesey (JIRA User)
Type Bug
Environment

Version 9.3 (9E145)

Swift 4.1

Additional Detail from JIRA
Votes 0
Component/s Standard Library
Labels Bug
Assignee @moiseev
Priority Medium

md5: 465ff5325f60aedb3bcc1562fda22cee

Issue Description:

In this code:

let lc = [1, nil].lazy

let fm = Array(lc.flatMap({ _ in return true }))

There is no warning in Swift 4.1. It seems like this should be a compactMap, not a flatMap.

It seems like the problem is with:

extension LazyCollectionProtocol where Self.Elements : BidirectionalCollection {
    public func flatMap<ElementOfResult>(_ transform: @escaping (Self.Elements.Element) -> ElementOfResult?) -> LazyMapCollection<LazyFilterCollection<LazyMapCollection<Self.Elements, ElementOfResult?>>, ElementOfResult>
}

I think this function should be deprecated and replaced with compactMap
@belkadan
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belkadan commented May 1, 2018

cc @moiseev

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moiseev mannequin commented May 3, 2018

plivesey (JIRA User) I.. can't find this definition in the codebase. All the wrong instances of flatMap(_: ) seem to be annotated appropriately.

@moiseev
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moiseev mannequin commented May 4, 2018

Ahh.. Found it! https://github.com/apple/swift/blob/swift-4.1-branch/stdlib/public/core/FlatMap.swift#L173-L182
For some reason the availability attribute did not make it into the swift-4.1-branch and slipped into the release.
Fixed in master and in swift-4.2-branch.

@swift-ci
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swift-ci commented May 4, 2018

Comment by Peter Livesey (JIRA)

Ah, great. Thanks for the info.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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@moiseev moiseev

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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 @swift-ci