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[SR-6977] NSObject inheritance causes: Error non-nominal type does not support explicit initialization #49525

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swift-ci opened this issue Feb 10, 2018 · 7 comments
Closed

[SR-6977] NSObject inheritance causes: Error non-nominal type does not support explicit initialization #49525

swift-ci opened this issue Feb 10, 2018 · 7 comments
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@slavapestov
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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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@swift-ci
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Previous ID SR-6977
Radar rdar://problem/37462507
Original Reporter ebg (JIRA User)
Type Bug
Status Closed
Resolution Done
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, TypeChecker
Assignee @slavapestov
Priority Medium

md5: 4187fdb70abb1858fa5854feea50ed46

Issue Description:

I'm trying to instantiate a generic type which is constrained to be a protocol (which includes the init method), which is constrained be a concrete UIView subclass. However the init throws the compiler error: non-nominal type 'ViewType' does not support explicit initialization. This is only the case when we make Self: UIView. If we constrain Self to a non-NSObject, the code compiles.

import UIKit

protocol ListModel {
}

protocol ListView where Self: UIView {
    init(model: ListModel)
}

class ListController<ViewType>: UIViewController where ViewType: ListView {

    func update(listModels: [ListModel]) {
        let views = listModels.map { (model: ListModel) -> UIView in
            let view: UIView = ViewType(model: model) // error
            return view
        }
        /** ... add UIViews as subviews */
    }
}

Expanded upon in the Swift forums:
https://forums.swift.org/t/error-non-nominal-type-does-not-support-explicit-initialization/9195
@belkadan
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@swift-ci create

@slavapestov
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Ooops, this is 'protocols inheriting from classes' and not what I thought it was.

@swift-ci
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Comment by Erich Graham (JIRA)

Any idea if this bug will be resolved in 4.2 or 5.0? This seems like a simple bug with bridging NSObjects, and is a pretty powerful use case for abstractions in UIKit code.

@slavapestov
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I just checked and the test case now works in 4.2. However, note that writing "protocol ListView where Self: UIView" is not really supported in 4.2. In future releases, you might have to write "protocol ListView : UIView", instead.

@swift-ci
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Comment by Erich Graham (JIRA)

Thanks Slava!

@AnnaZaks
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AnnaZaks mannequin commented Jul 23, 2019

ebg (JIRA User), Could you verify if the problem is fixed and if so move the JIRA to "Closed"?

Thanks!
Anna

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Comment by Erich Graham (JIRA)

Verified fixed

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
This issue was closed.
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@slavapestov slavapestov

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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@slavapestov @belkadan @swift-ci