Continue: static func() const; legal?

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3 total messages Started by Bret Pehrson Wed, 01 Nov 1995 20:34

#2385

Author: Bret Pehrson
Date: Wed, 01 Nov 1995 20:34

45 lines
1738 bytes

A while back I asked whether the following was legal:

class base
{
  static funkie(void) const;
};

I received two responses, both of which said (paraphrased):

It is not legal, and does not make sense because 'const' implies that 
the this pointer is constant, and since 'static' members do not have 
a this pointer, it is meaningless.

After some thought, I would like to repose the question:

Suppose:

class base
{
  static void lumpy(void) const;
  static int cLumps;
};
int base::cLumps = 0;


void base::lumpy(void)
{
  ++cLumps;
}


Now, since cLumps is a member of base, albeit static, making a static 
member function 'const' would mean that it does not change available 
class members (in this case, static member variables).

So, with this above sample, I can definitely see a legitimate need 
for static const member functions.

Legal or not?



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Re: Continue: static func() const; legal?

#2393

Author: Matt Austern
Date: Thu, 02 Nov 1995 02:30

31 lines
2321 bytes

In article <478k57$5gl@stellar.comnet.com> Bret Pehrson <BretP@strata3d.com> writes:

> Now, since cLumps is a member of base, albeit static, making a static 
> member function 'const' would mean that it does not change available 
> class members (in this case, static member variables).
> 
> So, with this above sample, I can definitely see a legitimate need 
> for static const member functions.

The thing you have to remember is that static member variables really
aren't particularly special in any way: from section 9.5.2 of the
draft standard it's pretty clear that static member variables are
almost exactly the same as global variables, except that the are in
class scope instead of namespace scope, and they obey class access
rules.

There's no way to declare a function such that it's prohibited from
modifying global variables; similarly, there's no way to declare a
function such that it's prohibited from modifying static member
variables.  Static member variables are really a notational
convenience more than anything else: pretty much anything you can do
with static member variables, you can also do with global variables
declared in a namespace.
-- 
  Matt Austern                             He showed his lower teeth.  "We 
  matt@physics.berkeley.edu                all have flaws," he said, "and 
  http://dogbert.lbl.gov/~matt             mine is being wicked."

[ comp.std.c++ is moderated.  Submission address: std-c++@ncar.ucar.edu.
  Contact address: std-c++-request@ncar.ucar.edu.  The moderation policy
  is summarized in http://dogbert.lbl.gov/~matt/std-c++/policy.html. ]

Re: Continue: static func() const; legal?

#2401

Author: Ralph Shnelvar
Date: Thu, 02 Nov 1995 23:29

27 lines
1547 bytes

matt@cyclops5.berkeley.edu (Matt Austern) wrote:

>In article <478k57$5gl@stellar.comnet.com> Bret Pehrson
><BretP@strata3d.com> writes:
>
>There's no way to declare a function such that it's prohibited from
>modifying global variables; similarly, there's no way to declare a
>function such that it's prohibited from modifying static member
>variables.

That's a double pity.

First, it is a pity that one cannot declare a function and say "You
can't access global variables.

Second, it is a pity that class static variables cannot be defined as
untouchable.

Thanks for pointing this counter-intuitive use of
	function() const
out.  I actually had to run a test compilation to believe you.

Ralph
---
[ comp.std.c++ is moderated.  Submission address: std-c++@ncar.ucar.edu.
  Contact address: std-c++-request@ncar.ucar.edu.  The moderation policy
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