Axel Freyn wrote:
Hi Patrick,
On Tue, Feb 02, 2010 at 09:56:19AM -0800, Patrick Horgan wrote:
There is also another possibilty you could maybe think about: If you
create an additional structure, which "caches" the pointer to A or B and
returns references to it, you can have this new structure living on the
stack - and do with it whatever you want (e.g. you can insert it into a
std::vector without problems):
struct Cache{
Cache( A* _a):a(_a){}
A *a;
A& operator()(){ return *a;}
};
I like this whole thing, but wouldn't operator* be more natural to
return the reference?
Even if we are probably quite off-topic now: Yes, you are absolutely
right. I only used () as, when I first (already a few years ago) wrote a
similar class (a bit more complex) which I wanted to use for fast
matrix-vector calculations, I realized a problem with "*": it can lead
to unresolved overloads when you write something like
class GeneralCache { ... };
class Cache : public GeneralCache { ... };
... operator * (const GeneralCache &, const GeneralCache & );
Yes, I see this, but this is the nature of the beast. Even without user
defined types you can get exactly this same problem and sometimes need
parenthesis to make clear what you mean. When you override operator()
people expect the meaning to be function or constructor.
Cache a, b, c;
c = a * b;
Now is "*" dereferencing b, or is it multiplying a and b?
Frustrating when you try to come up with a good example off the top of
your head and you can't think of one, huh? It always happens to me
too. Of course this would only make sense for the binary operator*, the
unary would one just be a syntax error, and current gcc would use the
binary one without warnings.
Patrick
