使 @MainActor 类或 actor 符合 Codable

Question

如何向需要与 MainActor 隔离的类添加 Codable 一致性？

例如，以下代码会给出编译器错误：

@MainActor final class MyClass: Codable {
    var value: Int
    
    enum CodingKeys: String, CodingKey {
        case value
    }
    
    init(from decoder: Decoder) throws { // <-- Compiler error: Initializer 'init(from:)' isolated to global actor 'MainActor' can not satisfy corresponding requirement from protocol 'Decodable'
        let data = try decoder.container(keyedBy: CodingKeys.self)
        self.value = try data.decode(Int.self, forKey: .value)
    }
    
    func encode(to encoder: Encoder) throws { // <-- Compiler error: Instance method 'encode(to:)' isolated to global actor 'MainActor' can not satisfy corresponding requirement from protocol 'Encodable'
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(value, forKey: .value)
    }
}

我现在确实很难理解演员和@MainActor！

Answer 1

您提供的类中没有任何内容需要与主要参与者隔离，因此不要将类作为一个整体进行隔离。如果您没有向我们展示其他确实需要与主要演员隔离的成员，请将他们隔离。

例子：

final class MyClass: Codable {
    private var value: Int
    @MainActor init(value: Int) {
        self.value = value
    }
    @MainActor func setMyValue(to newValue:Int) {
        self.value = newValue
    }
    @MainActor func getMyValue() -> Int {
        self.value
    }
    enum CodingKeys: String, CodingKey {
        case value
    }
    init(from decoder: Decoder) throws {
        let data = try decoder.container(keyedBy: CodingKeys.self)
        self.value = try data.decode(Int.self, forKey: .value)
    }
    func encode(to encoder: Encoder) throws { // <-- Compiler error: Instance method 'encode(to:)' isolated to global actor 'MainActor' can not satisfy corresponding requirement from protocol 'Encodable'
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(value, forKey: .value)
    }
}