Struct with protocol as property type does not conform to protocols ‘Decodable’ and ‘Encodable’.

huangapple
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英文:

Struct with protocol as property type does not conform to protocols 'Decodable' and 'Encodable'

问题

Here is the translation of the code you provided:

  1. 我有一个名为`UISectionModel`的结构体，只有一个名为`section`的属性，该属性遵循一个名为`UISectionProtocol`的协议，如下所示：
  3. ```swift
  4. struct UISectionModel: Codable {
  5.     let section: UISectionProtocol
  6. }

这是UISectionProtocol协议的实现：

  1. protocol UISectionProtocol: Codable {
  2.     var identifier: String? { get }
  3. }

正如您所看到的，我需要让UISectionModel遵循Codable协议，但我一直收到一个错误，指出它既不遵循Decodable也不遵循Encodable，尽管唯一的属性类型已经遵循了Codable。我怀疑这与这个类型是一个协议有关，但我无法确定导致错误出现的确切原因或如何修复它。

我尝试将section的类型替换为符合UISectionProtocol的枚举：

  1. struct UISectionModel: Codable {
  2.     let section: UIDefaultSection
  3. }
  5. enum UIDefaultSection: UISectionProtocol {
  6.     case imageSection(section: UIImageSection)
  7.     case labelSection(section: UILabelSection)
  8.     
  9.     var identifier: String? {
  10.         switch self {
  11.         case .imageSection(let section): return section.identifier
  12.         case .labelSection(let section): return section.identifier
  13.         }
  14.     }
  15. }

这使错误消失了，但我在思考section是否需要是符合UISectionProtocol的任何类型，而不仅仅限于UIDefaultSection。

  2. <details>
  3. <summary>英文:</summary>
  5. I have a struct `UISectionModel` with only one property `section`, which has a protocol `UISectionProtocol` for a type, as follows:

struct UISectionModel: Codable {
let section: UISectionProtocol
}

  1. Here is the implementation of the `UISectionProtocol` protocol:

protocol UISectionProtocol: Codable {
var identifier: String? { get }
}

  1. As you can see, I need `UISectionModel` to conform to the `Codable` protocol, but I keep getting an error stating that it does not conform to neither `Decodable` or `Encodable`, even though the only property&#39;s type is already conforming to `Codable`. I suspect it has to do with the fact that this type is a protocol, but I can&#39;t figure the exact reason that is causing the error to appear or how to fix it. 
  3. Would appreciate some insight!
  5. I tried replacing the type of `section` with an enum that conforms to `UISectionProtocol`:

struct UISectionModel: Codable {
let section: UIDefaultSection
}

enum UIDefaultSection: UISectionProtocol {
case imageSection(section: UIImageSection)
case labelSection(section: UILabelSection)

  1. var identifier: String? {
  2.     switch self {
  3.     case .imageSection(let section): return section.identifier
  4.     case .labelSection(let section): return section.identifier
  5.     }
  6. }

}

  1. This made the error go away, but I&#39;m thinking that `section` needs to be of any type that conforms to `UISectionProtocol`, instead of being limited only to `UIDefaultSection`.
  4. </details>
  7. # 答案1
  8. **得分**: 2
  10. 我认为问题在于您可能认为以下代码段：
  12. ```swift
  13. protocol UISectionProtocol: Codable

意味着UISectionProtocol符合Codable。但实际上它并不符合。协议不会符合协议。您可能想要一个泛型：

  1. struct SectionModel<T: SectionProtocol>: Codable {
  2.     let section: T
  3. }
  5. protocol SectionProtocol: Codable {
  6.     var identifier: String? { get }
  7. }

（请注意，我已经去掉了您的类型名称中非法的UI前缀；该前缀仅属于Apple。）

英文:

I think the problem is that you probably believe that saying

  1. protocol UISectionProtocol: Codable

means that UISectionProtocol conforms to Codable. it doesn't. A protocol does not conform to a protocol. You probably want a generic:

  1. struct SectionModel&lt;T: SectionProtocol&gt;: Codable {
  2.     let section: T
  3. }
  5. protocol SectionProtocol: Codable {
  6.     var identifier: String? { get }
  7. }

(Note that I have stripped the illegal UI prefix off your type names; that prefix belongs to Apple alone.)

答案2

得分: 1

你遇到的问题是由不符合 Codable 协议的协议引起的。当你在 UISectionModel 结构体中包含一个 UISectionProtocol 字段时，编译器无法保证所有符合类型也都是 Codable 的。

要解决这个问题，你可以将 UISectionModel 定义为泛型，并添加一个类型约束以确保 section 属性也是 Codable 的。以下是你代码的更新版本，我认为这可能会解决你的问题。

  1. protocol UISectionProtocol: Codable {
  2.     var identifier: String? { get }
  3. }
  5. struct UISectionModel<T: UISectionProtocol>: Codable where T: Codable {
  6.     let section: T
  7. }
  9. struct MySection: UISectionProtocol, Codable {
  10.     var identifier: String?
  11. }
英文:

The issue you experienced is caused by protocols that don't conform to Codable. When you include a UISectionProtocol field in your UISectionModel struct, the compiler cannot guarantee that all conforming types are also Codable.
To fix this problem you can make UISectionModel generic and add a type constraint to ensure the section property is also codable. Here is an updated version of your code. I think this may solve your issue.

  1. protocol UISectionProtocol: Codable {
  2.     var identifier: String? { get }
  3. }
  4. struct UISectionModel&lt;T: UISectionProtocol&gt;: Codable where T: Codable {
  5.     let section: T
  6. }
  8. struct MySection: UISectionProtocol, Codable {
  9.     var identifier: String?
  10. }

huangapple
  • 本文由 发表于 2023年6月12日 10:02:18
  • 转载请务必保留本文链接：https://go.coder-hub.com/76453259.html
  • codable
  • decodable
  • encodable
  • swift
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