Apply.swift

public protocol Apply {}

extension Apply where Self: Any {

  //let f = Foo().apply {
  //  $0.foo = 10
  //  $0.bar = "bar"
  //}
  public func apply(_ block: (inout Self) -> Void) -> Self {
    var copy = self
    block(&copy)
    return copy
  }

  //UserDefaults.standard.do {
  //  $0.set("abc", forKey: "username")
  //  $0.set("abc@hotmail.com", forKey: "email")
  //  $0.synchronize()
  //}
  public func `do`(_ block: (Self) -> Void) {
    block(self)
  }

  public func with<R>(_ receiver: Self, _ block: (Self) -> R) -> R {
    return block(receiver)
  }

}

struct Data {
  var f1: String = ""
  var f2: Int = 0
  var f3: [Double] = []
}

extension Data : Apply {}

let d = Data().apply { 
  $0.f1 = "hello"
  $0.f2 = 100
  $0.f3 = [1.0,2.0,3.0]
}

print(d)