Codable + default value

Codable+default.swift

protocol Init {
    init()
}

extension KeyedDecodingContainer {
    func decode<T: Codable & Init>(_ type: T.Type,
                forKey key: Key) throws -> T {
        try decodeIfPresent(type, forKey: key) ?? .init()
    }
}

test code
`enum B: Int, Codable {
case one = 1
case two = 2
}

extension B: Init {
init() {
self = .one
}
}

struct A: Decodable {
let b: B
}

let data = try JSONSerialization.data(withJSONObject: [:])
let a = try JSONDecoder().decode(A.self, from: data)
`