PropertyWrapper: Ignore codable properties

Example.swift

struct Foo: Codable {
    var name: String
    @Ignore var foo: Int?
}

let model = Foo(name: "Ian", foo: 42)
let data = try! JSONEncoder().encode(model)
print(String(data: data, encoding: .utf8)!) // {"name":"Ian"}


let json = """
{"name":"Ian","foo":42}
"""
let model = try! JSONDecoder().decode(Foo.self, from: Data(json.utf8))
print(model) // Foo(name: "Ian", foo: 42)

Ignore.swift

@propertyWrapper
struct Ignore<T> {
    var wrappedValue: T
}

extension Ignore: Encodable where T: Encodable { }
extension Ignore: Decodable where T: Decodable { }

extension KeyedEncodingContainer {
    mutating func encode<T: Encodable>(_ value: Ignore<T>, forKey key: KeyedEncodingContainer<K>.Key) throws { }
}

extension KeyedDecodingContainer {
    func decode<T: Decodable>(_ type: Ignore<T?>.Type, forKey key: KeyedDecodingContainer<K>.Key) throws -> Ignore<T?> {
        return try .init(wrappedValue: decodeIfPresent(T.self, forKey: key))
    }
}