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[SR-10592] ExpressibleByArrayLiteral won't compile on type nested in a generic type. #52992

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swift-ci opened this issue May 1, 2019 · 4 comments
Open

[SR-10592] ExpressibleByArrayLiteral won't compile on type nested in a generic type. #52992

swift-ci opened this issue May 1, 2019 · 4 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation type checker Area → compiler: Semantic analysis

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@swift-ci
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swift-ci commented May 1, 2019

Previous ID SR-10592
Radar None
Original Reporter Jaap (JIRA User)
Type Bug
Environment

MacOS 10.14.4

Xcode and command line tools 10.2.1

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

md5: f27798e55c6f49438c30d3b4a0ac8307

Issue Description:

I'm not able to use the ExpressibleByArrayLiteral Protocol when applying it to a nested type that has a parent type that works with a generic type. Some example code:

struct Dimension {
    var value: Int
}


extension Dimension: ExpressibleByIntegerLiteral {
    init(integerLiteral value: Int) {
        self.value = value
    }
}


struct Tensor<Element> {
    struct Shape {
        var dimensions: [Dimension]
    }
}


extension Tensor.Shape: ExpressibleByArrayLiteral {
    init(arrayLiteral elements: Dimension...) {
        self.dimensions = elements
    }
}


let shape: Tensor.Shape = [1,1,1]

The last line won't compile, giving the error:

Cannot convert value of type '[Int]' to specified type 'Tensor.Shape'

When removing the generic type <Element> from the Tensor struct, everything compiles.

Could be that I'm missing something, but I think this should just work right?
@belkadan
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belkadan commented May 1, 2019

It's the wrong error message, but the problem is that you haven't specified the type of Element for shape. Is it a Tensor<Int>.Shape or a Tensor<Float>.Shape?

Keeping this for the error message.

@belkadan
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belkadan commented May 1, 2019

cc @xedin

@swift-ci
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swift-ci commented May 1, 2019

Comment by Jaap Wijnen (JIRA)

But the type of Element, isn’t needed for the initialization of the shape object as Dimension is just a wrapper around an Int. Any way to circumvent this then?

@belkadan
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belkadan commented May 1, 2019

That's not how generics work in Swift. Tensor<Int>.Shape and Tensor<Float>.Shape are different types, and the compiler needs to know which one you're trying to make here. That's what it means to nest a type inside a generic type; if you don't want that behavior, you have to not nest it.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation type checker Area → compiler: Semantic analysis
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