无法使用类型为“(可解码，来自:数据)"的参数列表调用“解码" [英] Cannot invoke 'decode' with an argument list of type '(Decodable, from: Data)'

问题描述

我在操场上有以下示例代码.如果网络请求的结果符合Decodable协议，我想对该结果进行解码.

I have the following example code in a Playground. I want to decode the result of a network request if that result conforms to the Decodable protocol.

您知道为什么此代码不起作用吗?

Any idea why this code does not work?

protocol APIRequest {
    associatedtype Result
}

func execute<T: APIRequest>(request: T) {
    if let decodableResult = T.Result.self as? Decodable {
        try JSONDecoder().decode(decodableResult, from: Data())
    }
}

我在此行中收到错误Cannot invoke 'decode' with an argument list of type '(Decodable, from: Data)':try JSONDecoder().decode(decodableResult, from: Data())

I am getting the error Cannot invoke 'decode' with an argument list of type '(Decodable, from: Data)' on this line: try JSONDecoder().decode(decodableResult, from: Data())

任何输入都将不胜感激！

Any input is greatly appreciated!

推荐答案

JSONDecoder.decode(_:from:)方法需要符合Decodable的具体类型作为其输入参数.您需要向T.Result添加一个额外的类型约束，以使其成为Decodable.

The JSONDecoder.decode(_:from:) method requires a concrete type conforming to Decodable as its input argument. You need to add an extra type constraint to T.Result to make it Decodable.

func execute<T: APIRequest>(request: T) throws where T.Result: Decodable {
    try JSONDecoder().decode(T.Result.self, from: Data())
}

顺便说一句，尝试解码一个空的Data实例有什么意义?

Btw what's the point of trying to decode an empty Data instance?

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