KeyedDecodingContainerProtocol+Transform.swift

    /**
     Decodes a value of the given type for the given key, providing a transform closure that converts the decoded value into another type.
     
     - parameter type: The type of value to decode.
     - parameter key: The key that the decoded value is associated with.
     - parameter transform: A closure that transforms the decoded value into a value of a different type.
     
     - returns: The value that was returned by the `transform` closure.
     */
    func decode<T, R>(_ type: T.Type, forKey key: Self.Key, transform: (T) throws -> R) throws -> R where T : Decodable {
        let rawValue = try decode(type, forKey: key)
        return try transform(rawValue)
    }

    /**
     Decodes an array of values of the given type for the given key, providing a transform closure that converts each element of the decoded array
     into another type.
     
     - parameter type: The array type of values to decode.
     - parameter key: The key that the decoded array is associated with.
     - parameter transform: A closure that transforms the elements of the decoded array into a values of a different type.
     
     - returns: The value that was returned by the `transform` closure.
     */
    func decode<T, R>(_ type: [T].Type, forKey key: Self.Key, transform: (T) throws -> R) throws -> [R] where T : Decodable {
        let rawValues = try decode(type, forKey: key)
        return try rawValues.map { try transform($0) }
    }