AssociatedProjectedValue1.swift

import Cocoa

@propertyWrapper
public struct AssociatedValues<Value, Projection> {
  private var value: Value
  public var wrappedValue: Value { value }
  public var projectedValue: [String: Projection] = [:]
  
  public init(wrappedValue value: Value) {
    self.value = value
  }
}

public struct Test {
  @AssociatedValues<NSView, Any>
  public var view = NSView()
}

var t = Test()
print(t)
t.$view["weight"] = 4.2 // 4.2
t.$view["weight"] // 4.2
t.$view["weight"] = 5.9 // 5.9