const static member functions

[Rahul Joshi]

Hi,

Is it possible to define static member functions that are 'const',
i.e. they just read but do not modify the static data members of
a class? Declaring functions like:

class SomeClass {
static int read() const;
};

gives compiler errors, so it seems this is not directly supported.
Is there any other way in which I can get this effect?

Thanks,
Rahul

[Victor Bazarov]

Re: const static member functions

"Rahul Joshi" <rujoshi@studen ts.uiuc.edu> wrote...[color=blue]
> Is it possible to define static member functions that are 'const',
> i.e. they just read but do not modify the static data members of
> a class? Declaring functions like:
>
> class SomeClass {
> static int read() const;
> };
>
> gives compiler errors, so it seems this is not directly supported.[/color]

Correct. There is no object associated with the function (classes
are not objects in C++), so nothing to make obtain the const-ness
from.
[color=blue]
> Is there any other way in which I can get this effect?[/color]

What effect? Constant member functions are chosen in overload
resolution over non-constant ones when called with a constant
object (and vice versa). How would the compiler use the 'const'
with a function that doesn't have an object associated with it?

If you know that you're implementing a function that is supposed
not to change the static data, just don't change them.

Victor

[Shane Beasley]

Re: const static member functions

Rahul Joshi <rujoshi@studen ts.uiuc.edu> wrote in message news:<Pine.GSO. 4.31.0307151344 050.6212-100000@ux5.cso. uiuc.edu>...
[color=blue]
> Is it possible to define static member functions that are 'const',
> i.e. they just read but do not modify the static data members of
> a class?[/color]

Not really, no.
[color=blue]
> Declaring functions like:
>
> class SomeClass {
> static int read() const;
> };
>
> gives compiler errors, so it seems this is not directly supported.
> Is there any other way in which I can get this effect?[/color]

You could implement the Singleton design pattern (i.e., a single,
static instance of class SomeClass) and make read() a const,
non-static member function which operates on the instance. Or,
depending on your intentions, you could make the relevant static data
members const.

That's about it, really.

- Shane