Objects in OCaml are dictionary based, which means methods names must
be looked up in a table in order to get there addresses. Record fields
on the other hand are addressed directly. Take two files test.ml and
test2.ml:
test.ml:
 type b=
{
field:int
}
let a={field=1};;
print_int a.field

test2.ml
let a=object
 method field=1
end;;
print_int a#field

and dump there intermediate representation (-dlambda)

test.ml

(setglobal Test!
  (let (a/61 [0: 1])
    (seq (apply (field 27 (global Pervasives!)) (field 0 a/61))
      (makeblock 0 a/61))))

test2.ml

(setglobal Test2!
  (let
    (a/58
       (let
         (class/72 (apply (field 15 (global CamlinternalOO!)) [0: #"field"])
          obj_init/80
            (let
              (field/61
                 (apply (field 6 (global CamlinternalOO!)) class/72 #"field"))
              (seq
                (apply (field 10 (global CamlinternalOO!)) class/72
                  (makeblock 0 field/61 0a 1))
                (function env/74
                  (apply (field 23 (global CamlinternalOO!)) 0a class/72)))))
         (seq (apply (field 16 (global CamlinternalOO!)) class/72)
           (apply obj_init/80 0a))))
    (seq (apply (field 27 (global Pervasives!)) (send a/58 9671866))
      (makeblock 0 a/58))))

You can now understand where the performance issues comes from.

Cheers,
Till
On 6/24/07, Jon Harrop <jon@ffconsultancy.com> wrote:
> On Sunday 24 June 2007 16:14:54 tmp123@menta.net wrote:
> > Hello,
> >
> > I've tried to implement two equivalent small programs, the one using
> > class, the other one using records. The resulting execution times says
> > that class are 7-8 times slower than record (compiled with ocamlopt in a
> > Intel machine).
> >
> > Please, knows someone what I'm doing wrong?
>
> You aren't doing anything wrong.
>
> --
> Dr Jon D Harrop, Flying Frog Consultancy Ltd.
> The OCaml Journal
> http://www.ffconsultancy.com/products/ocaml_journal/?e
>
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-- 
http://till-varoquaux.blogspot.com/