在函数中使用 “any generic” 导致 “_ErrorCodeProtocol has no member” 错误。

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英文:

Swift: "any generic" in function causes "_ErrorCodeProtocol has no member" error

问题

Swift 5.8 使用 'any generic' 导致奇怪的错误 (_ErrorCodeProtocol)

你好！在我的宠物项目中，我想要减少 UIKit 的布局代码（我使用程序化的 UI 布局）。我的想法是为我的宠物项目创建一个用于最常见情况的枚举，例如：

  1. // view 是一个视图控制器的视图
  2. let searchArea = UIView()
  3. view.addSubview(searchArea)
  4. searchArea.applyConstraints(
  5.    .alignTopWithTop(of: guide),
  6.    .alignLeadingWithLeading(of: view),
  7.    .alignTrailingWithTrailing(of: view),
  8.    .alignHeight(with: view, mult: 0.1)
  9. )

我真的很喜欢它，比起下面的方式更好：

  1. let searchArea = UIView()
  2. view.addSubview(searchArea)
  3. object.translatesAutoresizingMaskIntoConstraints = false
  4. NSLayoutConstraint.activate([
  5.   searchArea.topAnchor.constraint(equalTo: view.topAnchor, constant: 0),
  6.   searchArea.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0),
  7.   searchArea.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0),
  8.   searchArea.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.1, constant: 0)
  9. ])

因为 UIViews 应该与其他 UIView 子视图以及 UIViewController 安全区域 (UILayoutGuide) 对齐，我使用了泛型来实现这一点：

  1. protocol UISnapable {
  2.     var leadingAnchor: NSLayoutXAxisAnchor { get }
  3.     // 这里包括 UIView 和 UILayoutGuide 同时拥有的其他锚点
  4.     var centerYAnchor: NSLayoutYAxisAnchor { get }
  5. }
  7. extension UIView: UISnapable {}
  8. extension UILayoutGuide: UISnapable {}
  10. enum Constraints<T: UISnapable> {
  11.     case alignTopWithTop(of: T, const: CGFloat = 0)
  12.     // 还有其他对齐情况
  13.     case setAspectWidth(ratio: CGFloat)
  14. }
  16. func applyConstraints(object: inout UIView, constraints: any UISnapable...) {
  17.     object.translatesAutoresizingMaskIntoConstraints = false
  18.     NSLayoutConstraint.activate(
  19.         // 将输入的可变参数转换为约束
  20.         constraints.map {
  21.             switch $0 {
  22.             case .alignTopWithTop(of: let of, const: let const):
  23.                 return object.topAnchor.constraint(
  24.                     equalTo: of.topAnchor,
  25.                     constant: const
  26.                 )
  27.             // 其他对齐情况
  28.             case .setAspectWidth(ratio: let ratio):
  29.                 return object.heightAnchor.constraint(
  30.                     equalTo: object.widthAnchor,
  31.                     multiplier: ratio
  32.                 )
  33.             }
  34.         }
  35.     )
  36. }

我在泛型 UISnapable 中使用了 "any" 关键字，因为它最近在 Swift 中为这种情况引入了。

但不幸的是，我遇到了错误 "Type _ErrorCodeProtocol has no member alignTopWithTop"。

我做错了什么？我不知道 _ErrorCodeProtocol 如何与我的泛型情况相关联。

我检查了 _ErrorCodeProtocol 的源代码，它指向 Foundation。但我没有在 Foundation 中找到它的声明。而且在 Apple 文档中也没有关于它的信息（https://developer.apple.com/search/?q=_ErrorCodeProtocol&type=Documentation）。

英文:

Swift 5.8 using 'any generic' causes strange error (_ErrorCodeProtocol)

Hello! In my Pet project I want to reduce layout code for UIKit (I'm using programmatic UI layout). The idea is to make enum for most used cases in my pet like:

  1. // view is a view controller&#39;s view
  2. let searchArea = UIView()
  3. view.addSubview(searchArea)
  4. searchArea.applyConstraints(
  5.    .alignTopWithTop(of: guide),
  6.    .alignLeadingWithLeading(of: view),
  7.    .alignTrailingWithTrailing(of: view),
  8.    .alignHeight(with: view, mult: 0.1)
  9. )

I really like it much more than:

  1. let searchArea = UIView()
  2. view.addSubview(searchArea)
  3. object.translatesAutoresizingMaskIntoConstraints = false
  4. NSLayoutConstraint.activate([
  5.   searchArea.topAnchor.constraint(equalTo: view.topAnchor, constant: 0),
  6.   searchArea.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0),
  7.   searchArea.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0),
  8.   searchArea.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.1, constant: 0)
  9. ])

Because UIViews should be aligned to other UIView childs as well as UIViewController safe Area (UILayoutGuide) I implemented this using generics:

  1. protocol UISnapable {
  2.     var leadingAnchor: NSLayoutXAxisAnchor { get }
  3.     // Here are other anchors that UIView and UILayoutGuide have at the same time
  4.     var centerYAnchor: NSLayoutYAxisAnchor { get }
  5. }
  8. extension UIView: UISnapable {}
  9. extension UILayoutGuide: UISnapable {}
  11. enum Constraints&lt;T: UISnapable&gt; {
  12.     case alignTopWithTop(of: T, const: CGFloat = 0)
  13.     // Other align cases here
  14.     case setAspectWidth(ratio: CGFloat)
  15. }
  18. func applyConstraints(object: inout UIView, constraints: any UISnapable...) {
  19.     object.translatesAutoresizingMaskIntoConstraints = false
  20.     NSLayoutConstraint.activate(
  21.         // Transforming input variadic to constraints
  22.         constraints.map {
  23.             switch $0 {
  24.             case .alignTopWithTop(of: let of, const: let const):
  25.                 return object.topAnchor.constraint(
  26.                     equalTo: of.topAnchor,
  27.                     constant: const
  28.                 )
  29.             // Other align cases here
  30.             case .setAspectWidth(ratio: let ratio):
  31.                 return object.heightAnchor.constraint(
  32.                     equalTo: object.widthAnchor,
  33.                     multiplier: ratio
  34.                 )
  35.             }
  36.         }
  37.     )
  38. }

I use "any" keyword for generic UISnapable as it's was recently introduced in Swift for such cases.

But unfortunately, I get error "Type _ErrorCodeProtocol has no member alignTopWithTop"

What I am doing wrong? I dunno how _ErrorCodeProtocol is connected to my generic case.

I've checked source of _ErrorCodeProtocol and it lead to Foundation. But I didn't find its declaration somewhere in foundation. Also I didn't find information on it in Apple docs (https://developer.apple.com/search/?q=_ErrorCodeProtocol&amp;type=Documentation)

答案1

得分: 1

你传递的是UISnapable列表，但你的意思是传递Constraints列表。在这种情况下，你将any放在了错误的位置。

我认为你的意思是这样的：

  1. // Constraints不是泛型，但在某些情况下可以容纳任何UISnapable
  2. enum Constraints {
  3.     // 使用`any UISnapable`而不是T
  4.     case alignTopWithTop(of: any UISnapable, const: CGFloat = 0)
  5.     // 在这里添加其他对齐情况
  6.     case setAspectWidth(ratio: CGFloat)
  7. }

然后方法是（请注意，这里的inout是不必要的；UIView是一个引用类型）：

  1. func applyConstraints(object: inout UIView, constraints: Constraints...) {
  2.                                                          ^^^^^^^^^^^

至于错误，编译器之所以困惑，是因为你正尝试switch一个非枚举类型（这里的$0是any UISnapable）。这个错误并不特别有帮助，并且与潜在问题无关。

英文:

You're passing a list of UISnapable, but you mean to pass a list of Constraints. In this case you're putting any in the wrong place.

What I believe you mean is this:

  1. // Constraints are not generic, but they can hold any UISnapable in some cases
  2. enum Constraints {
  3.     // Use `any UISnapable` rather than T
  4.     case alignTopWithTop(of: any UISnapable, const: CGFloat = 0)
  5.     // Other align cases here
  6.     case setAspectWidth(ratio: CGFloat)
  7. }

And then the method is (note that the inout here is unnecessary; UIView is a reference type):

  1. func applyConstraints(object: inout UIView, constraints: Constraints...) {
  2.                                                          ^^^^^^^^^^^

As for the error, the compiler is just getting confused because you're trying to switch on a non-enum ($0 here is any UISnapable). The error is not particularly helpful, and is not related to the underlying problem.

huangapple
  • 本文由 发表于 2023年5月30日 02:13:29
  • 转载请务必保留本文链接：https://go.coder-hub.com/76359530.html
  • any
  • generics
  • swift
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