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[SR-8951] Adding an init with matching type of another init should error with ambiguous reference #51456

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swift-ci opened this issue Oct 9, 2018 · 4 comments
Open

[SR-8951] Adding an init with matching type of another init should error with ambiguous reference #51456

swift-ci opened this issue Oct 9, 2018 · 4 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself regression swift 4.0

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@swift-ci
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swift-ci commented Oct 9, 2018

Previous ID SR-8951
Radar None
Original Reporter benasher44 (JIRA User)
Type Bug
Environment

macOS 10.13.6
Swift 4.2
Xcode 10.0 (10A255)

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, 4.0Regression
Assignee None
Priority Medium

md5: d8d439d344924ff347951eb1e0ab863e

Issue Description:

I went to add an extension to RangeReplaceableCollection today, and some tests started failing because some String s in our codebase started behaving funny. It turns out that a flatMap picked a different init without warning, which changed behavior and failed our tests.

Consider the following code:

import Foundation

//extension RangeReplaceableCollection {
//    public init(minimumCapacity: Int) {
//        self.init()
//        self.reserveCapacity(minimumCapacity)
//    }
//}

let num: Int? = 100
let str = num.flatMap(String.init) ?? ""

print("|\(str)|")

As is, this code prints |100|, but if you un-comment the extension, it prints ||. I would expect uncommenting the extension to cause a compiler error because that would make String.init ambiguous.
@swift-ci
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swift-ci commented Oct 9, 2018

Comment by Ben A (JIRA)

I worked around this by constraining the extension:

extension RangeReplaceableCollection where Self: ExpressibleByArrayLiteral

@swift-ci
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swift-ci commented Oct 9, 2018

Comment by Ben A (JIRA)

In trying figure out if/when this regressed, I changed the example a bit (String wasn't a RangeReplaceableCollection until Swift 4):

extension String {
    public init(minimumCapacity: Int) {
        self.init()
    }
}

let num: Int? = 100
let str = num.flatMap(String.init) ?? ""

print("|\(str)|")

This tweaked sample has the same issue in Swift 4.0 (prints differently depending on the presence of this extension), but it errors as expected in Swift 3.1:

error: ambiguous use of 'init'

@AnnaZaks
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AnnaZaks mannequin commented Oct 12, 2018

cc @airspeedswift, @DougGregor, @slavapestov

@swift-ci
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Comment by Ben A (JIRA)

Apologies for the overly-specific title. If someone has a better understanding of the impact here and how it likely spans beyond inits, feel free to update it!

@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. compiler The Swift compiler in itself regression swift 4.0
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