Where can I find more information about the use scenarios for "box"?
The Guide is terse:
>>
3.11 Boxes
A box is like a single-element vector. It can print as a quoted #&
followed by the printed form of the boxed value. A #& form can also be
used as an expression, but since the resulting box is constant, it has
practically no use.
<<
This explains what a box is, but not why or when you would want to use one.
I see box used as in this example from servlet-dispatch.rkt:
(define (dispatch/servlet
...
(define servlet-box (box #f))
...
(filter:make
...
(lambda (url)
(or (unbox servlet-box)
(let ([servlet
(parameterize ([current-custodian (make-custodian)]
[current-namespace
(make-servlet-namespace
#:additional-specs
default-module-specs)])
(if stateless?
(make-stateless.servlet
servlet-current-directory stuffer manager start)
(make-v2.servlet servlet-current-directory
manager start)))])
(set-box! servlet-box servlet)
servlet))))))
And I'm scratching my head, not understanding the point of using a box
as opposed to a simple non-boxed value.
My question isn't about this code per se; only an example. Generally,
in what situations would you use a box, and why?
Thank you.
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