在球拍中使用吸气剂和吸气剂实现封闭

Question

I had to miss a class and am having a bit of trouble figuring out how to get getters and setter to work in racket. I understand the concept in Java, but do not know how to apply it here. I can't seem to find anything similar or relevant online. If anyone would be kind enough to help get me started on the assignment below, I would really appreciate it:

(define (box x)
;; when the second item to cons is not
;; a list, we have a pair.
(cons
  (λ() x)
  (λ(y) (set! x y))))

(define (get-val bx)
 ((car bx)))
(define (set-val! bx new-val)
 ((cdr bx) new-val))


;; An employee object is represented as a list of
;; 3 setter-getter pairs
(define (Employee name position salary)
 (error "TBD"))
)


(define (get-name emp)
   (error "TBD")
 )
(define (set-name emp new-name)
  (error "TBD"))

(define (get-position emp)
  (error "TBD"))

(define (set-position emp new-pos)
  (error "TBD"))

(define (get-salary emp)
  (error "TBD"))
(define (set-salary emp new-pos)
  (error "TBD"))

(define prof (Employee "Austin" "Professor" 99999999999999999))

(get-name prof)
(get-position prof)
(get-salary prof)

(set-name prof "Tom the Mighty")
(set-position prof "Master of Time and Space")
(set-salary prof 12345678)

(get-name prof)
(get-position prof)
(get-salary prof)

Answer 1

Here's one possible implementation of Employee :

(define (Employee name position salary)
  (list (box name) (box position) (box salary)))

I'll let you define the rest of the functions. They should be straightforward (hint: combine get-val or set-val! with first , second , or third ).

Answer 2

Another possible solution is using a dispatch method.

(define (Employee name position salary)
  (define (get-employee-name)
    name)

;; Your code goes here

  (define (employee-dispatch msg)
    (cond ((eq? msg 'name) (get-employee-name))
          ;; other messages)))

This another way to represent an object. You can then create an employee and get the name as follows:

(define mp (Employee))
;; Get the name:
(mp 'name)
;; Set the name (not implemented above):
((mp 'set-name!) new-name)