在 Swift 中使用 Generic 作为属性类型时出错 [英] Error when using Generic as property type in Swift

问题描述

我在使用泛型作为属性的类型约束时遇到问题.这是一个非常简单的例子:

I'm having an issue when using a Generic as the type constraint on a property. Here is a very simple example:

import UIKit

class TSSignal<MessageType> {

    var message: MessageType?

    init() {
    }

}

在 Xcode 6 Beta (6A215l) 中，这不会编译.它失败并在底部出现以下错误:

In Xcode 6 Beta (6A215l) this will not compile. It fails with the following error at the bottom:

TSSignal.swift:13:9: error: unimplemented IR generation feature non-fixed class layout var message: MessageType? ^ LLVM ERROR: unimplemented IRGen feature! non-fixed class layout Command /Applications/Xcode6-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolc‌​hain/usr/bin/swift failed with exit code 

但是，如果我删除 var message: MessageType? 行，它会很好地构建.有任何想法吗?谢谢.

But, if I remove the line var message: MessageType? it will build fine. Any ideas? Thanks.

编辑 - 更改代码和错误以反映问题的当前状态

Edit - changed code and error to reflect current status of issue

编辑 - 相关:子类化 NSObject 和使用泛型时 Swift 编译错误

更新 (6/18/14) - 从 Xcode 6 - Beta 2 开始，该问题仍然存在

Update (6/18/14) - The issue still persists as of Xcode 6 - Beta 2

更新 (7/25/14) - 从 Xcode 6 - Beta 4 开始，问题仍然存在(感谢 @Ralfonso，我也验证了)

Update (7/25/14) - The issue still persists as of Xcode 6 - Beta 4 (thanks @Ralfonso, and I verified as well)

更新 (8/4/14) - 从 Xcode 6 - Beta 5 开始，该问题已修复！

Update (8/4/14) - The issue is FIXED as of Xcode 6 - Beta 5!

推荐答案

有一个没有类型擦除的解决方法(适用于 Xcode6-Beta2):

There is a workaround without type erasure (works as of Xcode6-Beta2):

import UIKit

class TSSignal<MessageType> {
    var _message: [MessageType] = []

    func getMessage() -> MessageType? {
        if _message.count > 0 {
            return _message[0]
        } else {
            return nil
        }
    }

    func setMessage(maybeMessage: MessageType?) {
        if let message = maybeMessage {
            _message = [message]
        } else {
            _message = []
        }
    }

    init() {
    }
}

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