[LC++]code reuse in const and non-const methods

[Dr Mark H Phillips]

On Wed, 2002-10-23 at 13:51, hursh wrote:
> Hi,
> 
> 	I'm trying to find declaration incantation that will allow me to reuse 
> the same implementation for a const and non-const method that return a 
> reference to *this.

Why must they return a reference to *this?  Couldn't you do a version
of neatThings() which is void, and use something else to give you *this?

> 
> class Foo {
> 	// neat things
> 	Foo& neatThings(){
> 		// do neat things here
> 		return *this;
> 	}
> 
> 	const Foo& neatThings() const{
> 		// do the same neat things
> 		return *this;
> 	}
> };
> 
> If I declare it const I can't use the return value in non-const ways 
> even if the instance is non-const.  If I don't declare it const, I can't 
> call it on const instances.  (Have I got this wrong?)

I'm not sure whether your design is best, but leaving that aside for
now... What you could do is:

class Foo {
public:
  Foo& neatThings() {
    doStuff();
    return *this;
  }
  const Foo& neatThings() const {
    doStuff();
    return *this;
  }
private:
  void doStuff() const {
    // do your neat things here
  }
};

Hope this helps.

Cheers,

Mark.

> 
> I don't want to maintain the same code in two places if I don't have 
> too.  I don't want to use a macro.  Templates just feel wrong here.  I 
> don't have it in the above example, but in my real world case the 
> methods are virtual.  Basically a draw routine.  No changes happen to 
> the object within the method(s), but it could be called in both consts 
> and non-const contexts.
> 
> Any ideas?  Thanks,
> Dan
> 
> 
> 
> _______________________________________________
> This is the Linux C++ Programming List
> : http://lists.linux.org.au/listinfo/tuxcpprogramming List
-- 
Dr Mark H Phillips
Research Analyst (Mathematician)

AUSTRICS - smarter scheduling solutions - www.austrics.com

Level 2, 50 Pirie Street, Adelaide SA 5000, Australia
Phone +61 8 8226 9850
Fax   +61 8 8231 4821
Email mark at austrics.com.au