RE: What is an object?

["Paul A. Steckler" <steck@cs.rice.edu>]

> BTW. - this is a slightly related question, but independent, and
> it isn't even a question...
> 
> The compiled, binary code of MrEd contains several dozens, perhaps
> more than a hundred occurrences of the string "ivar/proc". I wonder
> why...

OK, I can answer your non-question.

(ivar/proc object symbol) extracts the public member in the object named  
by the symbol.

'send' is just a macro that eventually expands to a use of ivar/proc.
Look up ivar/proc in Help Desk.

Sometimes using ivar/proc directly is useful, as in the following
example from the MysterX Dynamic HTML test suite:

---

(define filter-spec
  '(glow (strength 99) (enabled #t) (color "#ff00ff")))

(apply (ivar/proc txt 'set-filter!) filter-spec)

(let ([result (send txt filter)])
  (if (equal? result filter-spec)
      (printf "Checking filter~n")
      (error (format "filter test: Expected ~a, got ~a~n"
                     filter-spec result))))

---

Using ivar/proc allows me to apply the method set-filter! to a list.
If I'd used send, I'd have to put that information in arguments.
By using a list, I can put that information in one place, filter-spec, 
which is used to supply data to set-filter!, and again when 
checking the result.

-- Paul