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[SR-4304] Swift compiler unable to resolve correct overload of + operator for arrays in generic function #46887

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swift-ci opened this issue Mar 21, 2017 · 3 comments
Open

[SR-4304] Swift compiler unable to resolve correct overload of + operator for arrays in generic function #46887

swift-ci opened this issue Mar 21, 2017 · 3 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself type checker Area → compiler: Semantic analysis

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@swift-ci
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Previous ID SR-4304
Radar None
Original Reporter thm (JIRA User)
Type Bug
Environment

Xcode 8.2.1 (8C1002) with the included

$ swift --version
Apple Swift version 3.0.2 (swiftlang-800.0.63 clang-800.0.42.1)
Target: x86_64-apple-macosx10.9
Additional Detail from JIRA
Votes 1
Component/s Compiler
Labels Bug, TypeChecker
Assignee None
Priority Medium

md5: 929e460ad9d2931ec9a446f7be03c731

is blocked by:

  • SR-4309 Type inferring fails in expression with ?? and +

Issue Description:

I've had several problems with the plus operator so I decided to investigate and ended up with the following minimal example. When I compile

func f<T>(t: T) -> [T]
{
    return [t] + [t]
}

everything is fine. The compiler chooses this overload of the plus operator:

public func +<RRC1 : RangeReplaceableCollection, RRC2 : RangeReplaceableCollection
    where RRC1.Iterator.Element == RRC2.Iterator.Element>
    (lhs: RRC1, rhs: RRC2) -> RRC1

However, when I add another `+` to the game, I get this:

func f<T>(t: T) -> [T]
{
    return [t] + [t] + [t]
}

main.swift:30:9: error: cannot convert value of type '[T]' to expected argument type '[_]' (aka 'Array<_>')
    return [t] + [t] + [t]
           ^~~
               as! [_]

I found several ways to make this work, like for instance
@belkadan
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Still broken in master.

@rudkx
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rudkx commented Mar 22, 2017

@swift-ci

@rudkx
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rudkx commented Mar 22, 2017

There is a problem in the constraint optimizer that leads to our trying to force the type of the first '+' to T rather than [T].

@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 type checker Area → compiler: Semantic analysis
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@rudkx @belkadan @swift-ci