Partial<T>

Partial.swift

/// A wrapper for a partial representation of a `T`.
/// It can be constructed over time, then later used to
/// build a complete `T`
@dynamicMemberLookup
public struct Partial<T> {
    enum Error: Swift.Error {
        case invalid(PartialKeyPath<T>)
    }

    // MARK: - Private Properties
    private var data: [PartialKeyPath<T>: Any] = [:]

    // MARK: - Lifecycle
    public init() { }

    public subscript<U>(dynamicMember keyPath: KeyPath<T, U>) -> U? {
        get { return data[keyPath] as? U }
        set { data[keyPath] = newValue }
    }

    public func contains(_ keyPath: PartialKeyPath<T>) -> Bool {
        return data[keyPath] != nil
    }
    public mutating func combine(with other: Partial<T>) -> Partial<T> {
        for (key, value) in other.data {
            data[key] = value
        }
        return self
    }
}