> > >> This is not correct. Many strings are simply referenced several > > >> times. > > > > > > May I ask in which typical cases?
In an earlier version of our database (before we had things properly typed) many things were stored as strings. Thus a common ansistring may have had a reference count in the hundreds or even thousands. Most of the time, if I changed one of them, I would not want to change them all! But it saved a lot of memory to not be redundantly storing the same string. > > The most common one is probably assigning a function result to a > > variable or field. > > Is there increment of ref count (I think it does +1-1)? If no, passing the ref > cannot have any side-effect, so the copy_on_write scheme does not apply -- or > rather does not make any change if applied. This is plain reference copy. > The issue is rather for parameter passing, since here the original var > survives the call (see Martin's post). I believe it depends on the circumstance. It's been a while since I tested this, but IIRC, when a variable is passed-by-value the ref count is incremented, whereas if it is passed-by-reference the ref count is not incremented... as one should hope. In the case of the latter, this means that if the ref count is one, then copy-on-write is not needed, as there is only the one instance of the string-- so that can save some processor time. Back when I was dealing with enormous ansistrings that were frequently being changed, I spent considerable time researching this so as to figure out how to avoid unnecessary copy-on-writes. What I found is that the compiler's treatment of them is quite intuitive: there were no unpleasant surprises. I ended up changing a number of functions which took a value parameter and returned a result to instead take a reference parameter and change that. Have fun... ~David. _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
