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From: Oleg <oleg_inconnu@myrealbox.com>
To: caml-list@inria.fr
Subject: [Caml-list] Five Questions about Objects
Date: Sat, 13 Jul 2002 09:42:47 -0400
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Hi

A few questions on objects:

1) Why does the following code define a polymorphic class

 class point a b = 
    object 
      val x = a
      val y = b
    end;;

but adding "method get () = (x, y)" results in type errors only resolvable by 
specifying types with "class ['a, 'b] point (a:'a) (b:'b)" ? Why doesn't 

 class point a b = 
    object 
      val x = a
      val y = b
      method get () = (x, y)
    end;;

give me a polymorphic class?

2) What is the point of "class" and "new" keywords? How are they better than 
"let" ? E.g.

let point a b = 
  object
    val x = a
    val y = b
    method get () = (x, y)
  end;;

let my_point = point 3 7;; 
let many_float_points = Array.make 100 (point 4.0 3.0);;
?

3) Is it possible to access object datafields directly or only through 
methods?

4) Can I construct an object that the following function f would accept?
# let f a = a#m1 (); a#b#m2 ();;
val f : < b : < m2 : unit -> 'a; .. >; m1 : unit -> 'b; .. > -> 'a = <fun>

I tried the obvious (to me) and it doesn't work. What is the precedence and 
associativity of #?

5) What is the current state of marshalling objects? Is Jacques's patch going 
to be used in the upcoming O'Caml version or is it too untested? 

Thanks
Oleg
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