Swift 是否可以利用 Codable 从 Dictionary 初始化符合类型

这绝对是可能的，因为它是如何Foundation does it on Darwin:

open func decode<T : Decodable>(_ type: T.Type, from data: Data) throws -> T {
    let topLevel: Any
    do {
       topLevel = try JSONSerialization.jsonObject(with: data, options: .fragmentsAllowed)
    } catch {
        throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: [], debugDescription: "The given data was not valid JSON.", underlyingError: error))
    }

    let decoder = __JSONDecoder(referencing: topLevel, options: self.options)
    guard let value = try decoder.unbox(topLevel, as: type) else {
        throw DecodingError.valueNotFound(type, DecodingError.Context(codingPath: [], debugDescription: "The given data did not contain a top-level value."))
    }

    return value
}

您可以将任何内容传递给__JSONDecoder，它将对其进行解码.不幸的是，__JSONDecoder是私有的.但它也是开源的，所以这是可以修复的.太乏味了.

您需要复制大约1500 lines of __JSONDecoder implementation个和一些支持类型，删除__JSONDecoder前面的"Private"，然后您可以添加一个可以执行您想要的扩展:

extension JSONDecoder {
    fileprivate var options: _Options {
        return _Options(dateDecodingStrategy: dateDecodingStrategy,
                        dataDecodingStrategy: dataDecodingStrategy,
                        nonConformingFloatDecodingStrategy: nonConformingFloatDecodingStrategy,
                        keyDecodingStrategy: keyDecodingStrategy,
                        userInfo: userInfo)
    }

    func decode<T : Decodable>(_ type: T.Type, from topLevel: Any) throws -> T {
        let decoder = __JSONDecoder(referencing: topLevel, options: self.options)
        guard let value = try decoder.unbox(topLevel, as: type) else {
            throw DecodingError.valueNotFound(type, DecodingError.Context(codingPath: [], debugDescription: "The given data did not contain a top-level value."))
        }

        return value
    }
}

// And then it "just works":
let score = try JSONDecoder().decode(Score.self, from: scoreDictionary)