Guided Practice 10.1

Imagine we are working in a class called Class1%, with init-fields x, y, and z (all containing integers).

Consider the following method definition:

;; Number -> Class1%
;; GIVEN: a number u
;; RETURNS: an object just like this one, except that the new x field contains
;; x+y, and the new y field contains z+u.
(define/public (method1 u)
  (new Class1%
    [x (+ x y)]
    [y (+ z u)]
    [z z]))

Your task is to transform this into an imperative method using the Void transform. The new contract and purpose statement are:

;; Number -> Void
;; GIVEN: a number u
;; EFFECT: alters the fields of this object so that  the new x field
;; contains the value of x+y, and the new y field contains the value
;; of z+u.

;; EXAMPLE: if obj1 has fields x=10, y=20, and z=100, then calling
;; (send obj1 method1 5)
;; should leave obj1 with fields x=30, y=105, z=100.

Which of the following are correct versions of the new method?

;;; Version 1:

(define/public (method1 u)
  (new Class1%
    [x (+ x y)]
    [y (+ z u)]))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;; Version 2:

(define/public (method1 u)
  (set! x (+ x y))
  (set! y (+ z u)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;; Version 3:

(define/public (method1 u)
  (set! x (+ x y))
  (set! y (+ z u))
  (set! z z))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;; Version 4:

(define/public (method1 u)
  (set! x (+ x y))
  (set! z z)
  (set! y (+ z u)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;; Version 5:

(define/public (method1 u)
  (set! y (+ z u))
  (set! x (+ x y)))

[ANSWER]