Nested property wrappers with Swift

Appending.swift

// https://noahgilmore.com/blog/nesting-property-wrappers

import Cocoa

protocol Appendable {
    func appending(string: String) -> Self
}

extension String: Appendable {
    func appending(string: String) -> String {
        return self + string
    }
}

@propertyWrapper
struct Appending<T: Appendable> {
    private(set) var value: T
    let toAppend: String

    var wrappedValue: T {
        get { value }
        set { value = newValue.appending(string: toAppend) }
    }

    init(wrappedValue: T, _ toAppend: String) {
        self.value = wrappedValue
        self.toAppend = toAppend
    }
}

extension Appending: Appendable {
    func appending(string: String) -> Appending<T> {
        return Appending(wrappedValue: self.wrappedValue.appending(string: string), self.toAppend)
    }
}

struct Test {
    @Appending("!")
    @Appending("?")
    var name: String = ""

    init(_ name: String) {
        self.name = name
    }
}

var a = Test("Noah")
print(a.name)