在框架中声明结构的琐碎协议一致性 [英] Declare trivial protocol conformance for struct in a framework

问题描述

是否可以声明struct定义在框架中的struct符合我的应用程序中定义的协议?

Is it possible to declare that struct a struct, defined in a framework, trivially conforms to a protocol, defined in my app?

例如，我有一个API，用于为框架中建模的一些小部件声明结构:

Say, for example, I have an API that declares structs for a few widgets modelled in a framework:

public struct VagueWidget {
    public let temperature: Float
}

public struct SpecificWidget {
    public let calibratedTemperature: Float
    public let movingAverageTemperature: Float
}

public struct SuperSpecificWidget {
    public let surfaceTemperature: Float
    public let inferredCoreTemperature: Int?
}

然后在我的应用程序中，我想通过协议来概括这些内容.

And then in my application I want to generalise these by way of a protocol.

protocol Widget {
    var temperature: Float { get }
}

在我的应用程序中，我可以声明类似于API中的结构，并简单地声明它们符合协议.

In my application I can declare structs similar to those in the API, and trivially declare them as conforming to the protocol.

struct MockWidget {
    let temperature: Float
}

extension MockWidget: Widget {}

然后我可以声明框架中结构的协议一致性.

And then I can declare protocol conformance for the structs in the framework.

extension SuperSpecificWidget: Widget {
    var temperature: Float {
        get {
            return surfaceTemperature
        }
    }
}

extension SpecificWidget: Widget {
    var temperature: Float {
        get {
            return calibratedTemperature
        }
    }
}

extension VagueWidget: Widget {}

此代码可以编译，但不会链接.与应用程序中的MockWidget等效的框架中的VagueWidget符合标准，导致缺少符号:

This code compiles, but doesn't link. The trivially conforming VagueWidget in the framework which is equivalent to the MockWidget in the application results in a missing symbol:

Undefined symbols for architecture x86_64:
  "WidgetAPI.VagueWidget.temperature.getter : Swift.Float", referenced from:
   protocol witness for WidgetApp.Widget.temperature.getter : Swift.Float in conformance WidgetAPI.VagueWidget : WidgetApp.Widget in WidgetApp in AppModel.o

注释VagueWidget的琐碎协议一致性会生成可编译和运行的代码，但显然缺少所需的协议一致性.我在github上添加了示例项目.

Commenting out the trivial protocol conformance for the VagueWidget produces code that compiles and runs, but obviously missing the desired protocol conformance. I've added an example project on github.

更新:这似乎是一个已知问题.我已经提交了雷达，并且已作为 20648441 的副本关闭.

Update: This appears to be a known issue. I have filed a radar, and it was closed as a duplicate of 20648441.

推荐答案

发现的有趣错误.您和Scott H完成了所有工作，但想通过一些解决方法来解决问题:

Interesting bug you found. You and Scott H did all the work, but wanted to chime in with some workarounds:

1. 将模型从struct更改为class.不知道为什么会这样.

1. Change your models from struct to class. No idea why this works.

功能也可以使用(即func temperature() -> Float).

Functions also work (i.e. func temperature() -> Float).

两者都不尽人意.

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