Swift 4 中的通用解码器

Question

目前我正在使用这段代码来处理解码一些数据：

private func parseJSON(_ data: Data) throws -> [ParsedType] 
{
    let decoder = JSONDecoder()
    let parsed = try decoder.decode([ParsedType].self, from: data)
    return parsed
}
private func parsePlist(_ data: Data) throws -> [ParsedType] 
{
    let decoder = PropertyListDecoder()
    let parsed = try decoder.decode([ParsedType].self, from: data)
    return parsed
}

有没有办法创建一个泛型方法，将所有这些重复的代码联系在一起？

private func parse(_ data: Data, using decoder: /*Something*/) throws -> [ParsedType]
{
    let parsed = try decoder.decode([ParsedType].self, from: data)
    return parsed
}

Answer 1

如果你看一下JSONEncoder和PropertyListDecoder的swift stdlib，你会发现它们都共享一个方法

func decode<T: Decodable >(_ type: T.Type, from data: Data) throws -> T

因此，您可以创建一个具有所述方法的协议，并使两个解码器都符合它：

protocol DecoderType {
    func decode<T: Decodable >(_ type: T.Type, from data: Data) throws -> T
}
extension JSONDecoder: DecoderType { }
extension PropertyListDecoder: DecoderType { }

并像这样创建您的通用解析函数：

func parseData(_ data: Data, with decoder: DecoderType) throws ->  [ParsedType] {
    return try decoder.decode([ParsedType].self, from: data)
}

Answer 2

Decodable+Generic.swift

import Foundation
// Generic decode method for Decodable
func decode<T: Decodable>(data: Data) throws -> T {
    let decoder = JSONDecoder()
    return try decoder.decode(T.self, from: data)
}

可解码+通用测试.swift

import XCTest
@testable import YourProject
class Decodable_EncodableTests: XCTestCase {
    func testDecodableEncodable() {
        struct User: Decodable, Encodable {
            let name: String
            let sex: String
        }
        let json = """
        {
            "name": "Ronaldo",
            "sex": "Female"
        }
        """.data(using: .utf8)!
        do {
            // When
            let name = "Ronaldo"
            let sex = "Female"
            let user: User = try decode(data: json)
            // Then
            XCTAssertEqual(user.name, name)
            XCTAssertEqual(user.sex, sex)
        } catch let error {
            XCTFail(error.localizedDescription)
        }
    }
}