On 27.01.2013 19:09, Michael Van Canneyt wrote:
On Sun, 27 Jan 2013, Sven Barth wrote:
On 27.01.2013 16:27, luiz americo pereira camara wrote:
2013/1/26 Sven Barth <pascaldra...@googlemail.com>:
On 26.01.2013 12:52, Alexander Klenin wrote:
On Sat, Jan 26, 2013 at 10:50 PM, Sven Barth
<pascaldra...@googlemail.com> wrote:
Generics was implemented without my knowledge. I only found out when
suddenly
the classes unit had been changed to use them. After a horrible
discussion, this was reversed, because of the drop in speed you
got when
using generics.
Ah! So that is where those ifdefs in classes come from :) I always
wondered...
Is the drop still present/essential? Perhaps optimizer is now good
enough to drop those ifdefs?
Someone would need to test this. It could be that the generic
variant is
less optimal, because the generic list is built upon a list that
handles
pointers...
I did some test with generics last year:
http://lazarusroad.blogspot.com.br/2012/06/cost-of-using-generics.html
I would not use in classes unit
That's mostly about the "duplication" problem, which is known (maybe
I'll try to improve the situation some time). What would have been
more interesting is the performance of the generated code compared
with e.g. a TStringList or a TObjectList.
When I tested it, there was a 10% slowdown. It is the difference between
a direct pointer assignment vs. calling Move() for each assignment.
I just checked the code of TFPGList. It does not use Move if you look at
it correctly:
TFPGList.Add calls TFPSList.Add with the address of the argument.
TFPSList.Add in turn (basically) calls TFPSList.CopyItem which (in so
far you are right) is implemented using Move. But this method is virtual
and overridden in TFPGList where it's an assignment between dereferenced
pointers to the generic type T.
But maybe it would still be faster if TFPGList would not be derived from
TFPSList, but completely implement the list handling itself with an
"array of T" and using just assignments. It could be that all those
virtual method calls are the "problem" here...
Regardless, I don't see the need of replacing proven code with generics
just as a showcase for generics. If it ain't broken, don't fix it.
As I just wrote to luiz: I'm not suggesting to change anything in
Classes regarding usage of generics. I'm just curious regarding their
performance behavior.
Regards,
Sven
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