Ramifications of const

[eao197]

On Wed, 13 Jun 2007 16:13:01 +0400, Georg Wrede <georg at nospam.org> wrote:

<...skipped...>

> Conclusion
>
> For the purposes of language development, we now have two attributes for  
> each function: does it change its arguments, and does it change anything  
> else. I'd actually like to have these incorporated into the function  
> signature. A function can only be Pure if all the functions it calls are  
> Pure (i.e. do not change anything) and it is Pure itself.

That all is already in C++:

class Demo {
public :
   // Does not change anything in the Demo instance.
   void f() const;
   // Changes something in the Demo instance.
   void f1();

   // Does not change any argument.
   // Changes something in the Demo instance.
   void f2( int a, const char * b, const Something & c );

   // Does not change any argument.
   // Does not change anything in the Demo instance.
   void f3( int a, const char * b, const Something & c ) const;

   // Changes a, b and c.
   // Changes something in the Demo instance.
   void f4( int & a, char * b, Something & c );
   // Changes a, b and c.
   // Does not change anything in the Demo instance.
   void f5( int & a, char * b, Something & c ) const;
};

Yes, there are possible changes to some global variables or to mutable  
members of Demo.

> It might be useful to have "does chanege its arguments" as a flag which  
> can quickly be checked during compilation, even if it is deducable from  
> the argument declarations. This may speed things up. But the *more*  
> important flag would be whether the function may change "external"  
> things. This is hard to see without a flag in the signature.

I think if someone want to have 'pure functions' then it is better to look  
to functional programming languages.

-- 
Regards,
Yauheni Akhotnikau