如何創建滿足通用要求的實體

我創建了以下代碼，除了 TestDBAPI 的定義外，一切正常。

當我想創建一個符合 DBAPIProtocol 協議的型別時，總是無法生成滿足泛型約束的型別實體

請問，如何定義TestNoteFetcher 來滿足DBAPIProtocol 的協議要求。

ps：希望在DBAPIProtocol中能保持泛型定義的靈活性

謝謝

import Combine

// For Value

public enum WrappedID: Equatable, Identifiable, Sendable, Hashable {
    case string(String)
    case integer(Int)

    public var id: Self {
        self
    }
}

public protocol BaseValueProtocol: Equatable, Identifiable, Sendable {
    var id: WrappedID { get }
}

public struct Note: BaseValueProtocol {
    public var id: WrappedID
    public var index: Int

    public init(id: WrappedID, index: Int) {
        self.id = id
        self.index = index
    }
}

// For Object 

public protocol ConvertibleValueObservableObject<Value>: ObservableObject, Equatable, Identifiable where ID == WrappedID {
    associatedtype Value: BaseValueProtocol
    func convertToValueType() -> Value
}

public final class TestNote: ConvertibleValueObservableObject {
    public static func == (lhs: TestNote, rhs: TestNote) -> Bool {
        true
    }

    public var id: WrappedID {
        .integer(1)
    }

    public func convertToValueType() -> Note {
        .init(id: .integer(1), index: 0)
    }
}

// For Fetcher

public protocol ObjectFetcherProtocol<Object,ConvertValue> {
    associatedtype ConvertValue: BaseValueProtocol
    associatedtype Object: ConvertibleValueObservableObject<ConvertValue>
    var stream: AsyncPublisher<AnyPublisher<[Object], Never>> { get }
}

public final class TestNoteFetcher: ObjectFetcherProtocol {
    public typealias ConvertValue = Note
    public typealias Object = TestNote

    public var stream: AsyncPublisher<AnyPublisher<[TestNote], Never>> {
        sender.eraseToAnyPublisher().values
    }

    public var sender: CurrentValueSubject<[TestNote], Never>
    public init(_ notes: [TestNote] = []) {
        sender = .init(notes)
    }
}

// For API
public protocol DBAPIProtocol {
    var notesFetcher: () async -> any ObjectFetcherProtocol<any ConvertibleValueObservableObject<Note>, Note> { get set }
}

// get error in here . Cannot convert value of type 'TestNoteFetcher.Object' (aka 'TestNote') to closure result type 'any ConvertibleValueObservableObject<Note>'

public final class TestDBAPI: DBAPIProtocol {
    public var notesFetcher: () async -> any ObjectFetcherProtocol<any ConvertibleValueObservableObject<Note>, Note> = {
        TestNoteFetcher([])
    }
}

uj5u.com熱心網友回復：

由于您的閉包回傳太多anys，編譯器會感到困惑并告訴您 that TestNoteFetcherdoesn't conform any ObjectFetcherProtocol。泛型是您的朋友，您可以使用它associatedtype來跳過所有這些代碼并解決問題：

public protocol DBAPIProtocol {
    associatedtype Fetcher: ObjectFetcherProtocol
    var notesFetcher: () async -> Fetcher { get set }
}
public final class TestDBAPI: DBAPIProtocol {
    public var notesFetcher: () async -> TestNoteFetcher = {
        TestNoteFetcher([])
    }
}

uj5u.com熱心網友回復：

有時問題就在我面前，但我確實對此視而不見。感謝您的提醒。我對這部分代碼進行了更改，它現在可以作業了。

public protocol ObjectFetcherProtocol<ConvertValue> {
    associatedtype ConvertValue: BaseValueProtocol
    var stream: AsyncPublisher<AnyPublisher<[any ConvertibleValueObservableObject<ConvertValue>], Never>> { get }
}

public final class TestNoteFetcher: ObjectFetcherProtocol {

    public var stream: AsyncPublisher<AnyPublisher<[any ConvertibleValueObservableObject<Note>], Never>> {
        sender.eraseToAnyPublisher().values
    }

    public var sender: CurrentValueSubject<[any ConvertibleValueObservableObject<Note>], Never>
    public init(_ notes: [any ConvertibleValueObservableObject<Note>] = []) {
        sender = .init(notes)
    }
}

這樣，我仍然可以保持 DBAPIProtocol 中定義的靈活性，而無需引入關聯型別

標籤：迅速仿制药

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