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From: Goswin von Brederlow <goswin-v-b@web.de>
To: Guillaume Hennequin <gje.hennequin@gmail.com>
Cc: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] mixed functional / object style
References: <d8e32b760904180748h25b5dc06t3e204fbdc8caafde@mail.gmail.com>
Date: Mon, 20 Apr 2009 08:14:34 +0200
In-Reply-To: <d8e32b760904180748h25b5dc06t3e204fbdc8caafde@mail.gmail.com>
	(Guillaume Hennequin's message of "Sat, 18 Apr 2009 16:48:23 +0200")
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X-Spam: no; 0.00; guillaume:01 val:01 mutable:01 val:01 mutable:01 guillaume:01 byte:01 const:01 mfg:98 caml-list:01 writes:01 define:02 define:02 functional:02 variables:02 

Guillaume Hennequin <gje.hennequin@gmail.com> writes:

> Dear list,
> this is a somewhat naive question
> let's define
> class a = object
>  val mutable v = ...
>  method v = v
>  method m = something that uses v
> end ;;
> now assume that I want to create a lot of those a objects, so many that I may
> encounter memory problems.
> I thought the following would be better, memory wise, but when I test it
> doesn't seem to be the case
> class a = object
>  val mutable v = ...
>  method v = v
> end ;;
> and instead of each object having its own method m, I define it separately
> let m x = something that calls x#v
> This question is somewhat equivalent to: what is the memory consumption of a
> simple method
> method m = let _ = self#v in () ??
> Thanks a lot
> Guillaume.

A class is a reference to the virtual table of a class and its
instance variables. There is exactly one virtual table for every class
you declrare and all instances of that class share the same virtual
table. All the methods are listed in that one virtual table.

So a method will cost you 4 or 8 byte (or maybe more, don't know how
big the entry for a method is) but it will be something small and
const no matter how many instances you have.

MfG
        Goswin