Extensions giving Swift's decodable API type inference super powers

decodable.swift

// Private supporting types
private struct AnyCodingKey: CodingKey {
    var stringValue: String
    var intValue: Int?

    init(_ string: String) {
        stringValue = string
    }

    init?(stringValue: String) {
        self.stringValue = stringValue
    }

    init?(intValue: Int) {
        self.intValue = intValue
        self.stringValue = String(intValue)
    }
}

// Safe Decoding Container
public struct SafeDecodingContainer<Base: Decodable>: Decodable {
    public let value: Base?
    public init(from decoder: Decoder) throws {
        do {
            let container = try decoder.singleValueContainer()
            self.value = try container.decode(Base.self)
        } catch {
            print("Mapping ERROR: \(error)")
            self.value = nil
        }
    }
}

//Helpers
public extension Decoder {
    func decode<T: Decodable>(_ key: String, as type: T.Type = T.self) throws -> T {
        return try decode(AnyCodingKey(key), as: type)
    }

    func decode<T: Decodable, K: CodingKey>(_ key: K, as type: T.Type = T.self) throws -> T {
        let container = try self.container(keyedBy: K.self)
        return try container.decode(type, forKey: key)
    }

    func decodeGuard<T: Decodable>(_ key: String) throws -> T? {
        return try? self.decodeGuard(T.self, forKey: AnyCodingKey(key))
    }

    func decodeGuard<T: Decodable, K: CodingKey>(_ type: T.Type, forKey key: K) throws -> T? {
        let container = try? self.container(keyedBy: K.self)
        return tryOrNil { (try container?.decode(T.self, forKey: key)) }
    }

    func decodeGuardArray<T: Decodable>(_ key: String) throws -> [T] {
        return try decodeGuardArray(T.self, forKey: AnyCodingKey(key))
    }

    func decodeGuardArray<T: Decodable, K: CodingKey>(_ type: T.Type, forKey key: K) throws -> [T] {
        let container = try? self.container(keyedBy: K.self)
        let array = tryOrNil { (try container?.decode([T].self, forKey: key)) }
        return array?.compactMap { $0 } ?? []
    }
}

// example code
public struct SaveDecodeClass: Codable {
    public var token: String = ""
    public var urlString: String = ""

    public init(from decoder: Decoder) throws {
        token = try decoder.decodeGuard("token") ?? ""
        urlString = try decoder.decodeGuard("urlString") ?? ""
    }
}