Property wrappers that emulate C++ references

UnsafeReference.swift

@propertyWrapper
struct UnsafeReference<T> {
  public let address: UnsafePointer<T>
  var projectedValue: Self { self }
  init(_ address: UnsafePointer<T>) {
    self.address = address
  }
  var wrappedValue: T {
    get { address.pointee }
  }
}

@propertyWrapper
struct UnsafeMutableReference<T> {
  public let address: UnsafeMutablePointer<T>
  var projectedValue: Self { self }
  init(_ address: UnsafeMutablePointer<T>) {
    self.address = address
  }
  var wrappedValue: T {
    get { address.pointee }
    nonmutating _modify { yield &address.pointee }
    nonmutating set { address.pointee = newValue }
  }
}

struct W {
  init(a: UnsafePointer<Int>, b: UnsafeMutablePointer<Int>) {
    self._a = UnsafeReference(a)
    self._b = UnsafeMutableReference(b)
  }
  @UnsafeReference var a: Int
  @UnsafeMutableReference var b: Int
}

var x = 3
var y = 4

let z = W(a: &x, b: &y)
print(z.a, z.b)
z.b = 5
print(z.a, z.b)

func f(_ p: UnsafePointer<Int>) { print(p.pointee) }
print(z.$a)
print(z.$b)
f(z.$a.address)
f(&z.b)