An Experiment With Changeable Writers

Changeable.swift

// An experiment with isolating the key path writing mechanism
public struct Changeable<T> {
    public let value: T
    public let hasChanged: Bool

    public static func write<U: Equatable>(_ keyPath: WritableKeyPath<T, U>, _ value: U) -> (inout T) -> Changeable<T> {
        return { whole in
            let changed = whole[keyPath: keyPath] != value
            if changed {
                whole[keyPath: keyPath] = value
            }
            return Changeable(value: whole, hasChanged: changed)
        }
    }
}