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[SR-6211] type-inference fails through Optionals #48763

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weissi opened this issue Oct 24, 2017 · 2 comments
Open

[SR-6211] type-inference fails through Optionals #48763

weissi opened this issue Oct 24, 2017 · 2 comments
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@xedin
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compiler The Swift compiler in itself improvement type checker Area → compiler: Semantic analysis

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@weissi
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weissi commented Oct 24, 2017

Previous ID SR-6211
Radar None
Original Reporter @weissi
Type Improvement
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Improvement, TypeChecker
Assignee @xedin
Priority Medium

md5: 8e8a1c55fe146af0611d8368222697ed

Issue Description:

this small example program

public struct Bar {
    public init?() {
        return nil
    }
}

let x: Bar = .init()!
let y: Bar? = .init()

should even with Swift's local-only type-inference be inferred I believe, however the type-checker fails on both x and y :'(

test2.swift:7:21: error: type of expression is ambiguous without more context
let x: Bar = .init()!
             ~~~~~~~^
test2.swift:8:16: error: value of optional type 'Bar' not unwrapped; did you mean to use '!' or '?'?
let y: Bar? = .init()
               ^
                     !

for

$ swiftc --version
Apple Swift version 4.0.1 (swiftlang-900.0.66 clang-900.0.37)
Target: x86_64-apple-macosx10.9

and

Apple Swift version 4.1-dev (LLVM f35a4270ce, Clang bb20a94e86, Swift e4ddd564b9)
Target: x86_64-apple-darwin17.2.0
@belkadan
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Hm. Swift's inference says that the "return type" must exactly match the contextual type, so it's not surprising that this isn't supported. In particular, your second statement let y: Bar? = .init() could indicate an initializer defined on Optional, not on Bar. But we could consider adding something like this.

cc @xedin, @rudkx

@weissi
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weissi commented Apr 20, 2018

same in swift 4.1 release

$ swiftc test.swift
test.swift:7:21: error: type of expression is ambiguous without more context
let x: Bar = .init()!
             ~~~~~~~^
test.swift:8:16: error: value of optional type 'Bar' not unwrapped; did you mean to use '!' or '?'?
let y: Bar? = .init()
               ^
                     !

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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compiler The Swift compiler in itself improvement type checker Area → compiler: Semantic analysis
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@weissi @belkadan