Re: ROOT collections
Pasha Murat (murat@cdfsga.fnal.gov)
Sat, 11 Oct 1997 16:03:59 GMT
Fons Rademakers writes:
> > - how does the TObjArray know the number of elements in it? It is smart:
> > it doesn't do compression when one of its objects is deleted therefore
> > it allows "holes" in its structure.
> > Does it mean that to get the number of objects in TObjArray one has to
> > calculate this number explicitly by iterating over the collection each time
> > he needs it?
> >
> The are two cases:
> - no holes: TObjArray::GetEntriesFast() returns number of objects in
> array. Note: this is <= size of array (returned by TObjArray::Capacity()
> or GetSize()).
> - holes: TObjArray::GetEntries() returns number of objects in array
> (done by looping over array, thus expensive).
>
Hi Fons,
wouldn't it make sense to have in TObjArray (or in one of its base collection
classes ?) one more data member - number of objects in the array? In terms of
timind efficiency this doesn't add much - just one increment/decrement per
insertion/deletion. On the other hand it is extremely useful to have number of
objects in the collection as a data member and not only as a result of
calculation.
Regards, Pasha.