[boost] Re: Re: Re: why is operator() not const in random numbergenerators?

From: Thorsten Ottosen (nesotto_at_[hidden])
Date: 2003-04-16 09:25:44

----- Original Message -----
From: "Matthias Troyer" <troyer_at_[hidden]>
Newsgroups: gmane.comp.lib.boost.devel
Sent: Wednesday, April 16, 2003 1:44 PM
Subject: Re: Re: Re: why is operator() not const in random numbergenerators?

>
> On Tuesday, April 15, 2003, at 05:39 PM, Thorsten Ottosen wrote:
[snip]
> > 2) After all, a client don't care what random number he gets, only
> > that he
> > gets one. The right result of a call to rand() is not that it is a
> > particular random number, but that it's a random number. If the order
> > of the
> > sequence is important, that is still achievable if operator() is
> > const, it
> > is just not enforced by the compiler.
>
> Here I disagree. I actually do care very much about what number I get.
> There are several application where it is of essential importance to
> get the identical sequence again. I thus want to have control over
> where the internal state of the generator is changed - and that's where
> const comes in.

you still have control, but the compiler doesn't. The compiler cannot warn
you if you
use the random number generator somewhere else. But the same situation
arises if I declare
my variable mutable. Thus the only effect I get from a non-const operator is
that I need to prefix my member variable
with mutable. (This issue would disappear if I make a local variable instead
of a member variable, though)

> > 3) so (as seen from the client in 99% of the time) what is really the
> > benefit of having a non-const operator() .?
>
> et me ask differently: what is the benefit of making it const?

no mutable.

regards

Thorsten