Changeable.swift

public protocol Changeable {}

extension Changeable {
	/// Calls the `changes` closure passing the receiver value as an `inout` parameter. The final value of the argument
	/// after the `changes` closure returns is then returned from this method. Benefits to using this function come
	/// when used against value types.
	///
	/// Example:
	///
	/// 	extension UIEdgeInsets: Changeable {}
	/// 	let justBottomInsets = UIEdgeInsets.zero.applying({ $0.bottom = 8 })
	public func applying(_ changes: (inout Self) -> Void) -> Self {
		var newValue = self
		changes(&newValue)
		return newValue
	}

	/// Mutates the receiver in-place by calling the `changes` closure and passing the receiver value as an `inout`
	/// parameter. The final value of the argument after the `changes` closure returns will replace the receiver.
	/// Benefits to using this function come when used against value types.
	///
	/// Example:
	///
	/// 	extension UIEdgeInsets: Changeable {}
	///		var insets = UIEdgeInsets.zero
	///		insets.apply({ $0.bottom = 8 })
	public mutating func apply(_ changes: (inout Self) -> Void) {
		let newValue = applying(changes)
		self = newValue
	}
}

extension MutableCollection where Element: Changeable {
	/// Returns a collection of type `Self` with each element having `elementChanges` applied to it.
	public func applyingToElements(_ elementChanges: (inout Element) -> Void) -> Self {
		var newValue = self
		for index in newValue.indices {
			newValue[index].apply(elementChanges)
		}
		return newValue
	}

	/// Mutates the collection in-place with each element having `elementChanges` applied to it.
	public mutating func applyToElements(_ elementChanges: (inout Element) -> Void) {
		let newValue = applyingToElements(elementChanges)
		self = newValue
	}
}