Re: "pointers" to methods

[Gerd Stolpmann <gerd@gerd-stolpmann.de>]

On Tue, 06 Feb 2001, Mattias Waldau wrote:
>In the following code I would like to apply the method inc or dec to the
>object obj. However, what is the syntax I should use? At all comments below
>the compilation fails.

You can use partially evaluated method calls as pointers to methods. However,
this works only for methods with at least one argument:

let main() =
  let obj = new class1 in 
  let method_to_call =
    if Random.int 2 = 0 then
      obj # inc
    else 
      obj # dec
  in
  method_to_call 2; 
  obj # get()
;;

For methods without arguments, one has to explicitly create a function
representing the pointer. If inc and dec had no argument:

let main() =
  let obj = new class1 in 
  let method_to_call =
    if Random.int 2 = 0 then
      (fun () -> obj # inc)
    else 
      (fun () -> obj # dec)
  in
  method_to_call (); 
  obj # get()
;;

>class class1 =
>  object (self)
>    val mutable x = 1
>    method inc step = x <- x+step    
>    method dec step = x <- x+step
>    method get () = x
>  end
>
>let main () =
>  let method_to_call =
>    if Random.int 2 = 0 then 
>      inc   (* pointer to inc-method in class1 *)
>    else
>      dec   (* pointer to dec-method in class1 *)
>  in
>  let obj = new class1 in
>  obj#method_to_call 2;    (* apply pointer to method in class1 *)
>  obj#get ()
>

Gerd
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