oop - 我可以在 Racket 类中定义静态字段吗？

Question

我找不到在 Racket 中定义静态字段的方法。通过静态，我的意思是属于整个类而不是实例的字段。

(define counter% (class object%  
  (field (current-count 0))
  (super-new)

  (define/public (get-count)
    current-count)

  (define/public (next) 
    (set! current-count (+ current-count 1))
    (set! total (+ total 1))
    (list current-count total))))

(define c1 (new counter%))
(define c2 (new counter%))

(send c1 next)
(send c1 next)
(send c1 next)
(send c2 next)

所以本例中的total应该是一个静态字段，输出应该是:

'(1 1)
'(2 2)
'(3 3)
'(1 4)

Answer 1

这个解决方案怎么样？

#lang racket

(define counter%
  (let ([total 0])
    (class object%  
      (field (current-count 0))
      (super-new)

      (define/public (get-count)
        current-count)

      (define/public (next) 
        (set! current-count (+ current-count 1))
        (set! total (+ total 1))
        (list current-count total)))))

(define c1 (new counter%))
(define c2 (new counter%))

(send c1 next)
(send c1 next)
(send c1 next)
(send c2 next)