Re: MakeClass

Jacek M. Holeczek (holeczek@us.edu.pl)
Mon, 19 Apr 1999 17:48:17 +0200 (MET DST)

Hi,
Thanks for your reply.
> However, there are several problems with your implementation:
> - It is only valid for trivial TNtuples.
> - a branch cannot be an array (even static).
> - a branch cannot be an object.
As I have already written :
> > For the time being the MakeClass.cxx macro is quite dumb.
> > Feel free to add something to it ... .
Well, I hoped you could have a look at it and add something ... . :-)
Anyhow, I have just sent a modified MakeClass.cxx macro which might work
( or not ) for other cases, too.
> - reading the code is made more difficult.
For me, not really - 'leaf()' is not so much different from 'leaf'.
> - you introduce a performance penalty.
How much ? A call of a function against an access of a variable ?
As I have already written :
> > ( Of course, I know - calling a function is always slower then accessing
> > directly a variable, but ... if I subtract the time spent to find missing
> > SetBranchStatus and the time spent to load unneeded branches ... .)
I should also add here, that the decision to "load" ( or not ) a branch,
happens on an event by event basis. One "loads" only these branches that
are currently required.
If one uses a specific "leaf" many times in ones routine, it's just enough
to write 'register int leafleaf; leafleaf=leaf(); ...', and then one can
use the 'leafleaf' as many times as one wants in the routine. The
"performance penalty" of calling a function ( once ) is negligible.
> I have in mind an automatic algorithm similar to the one we implemented
> ( ... )
This might be nice.
But, do you mean that every leaf name that the algorithm finds will be
added into SetBranchStatus ? Will you "detect" leaves that will never be
accessed ? Or will you detect that for a particular event(s) some leaves
are not accessed, while some others do ? Or how do you want to deal with
cases where leaf names are "computed" on the fly ( these are just simple
C strings, you can do everything with them )?
And then comes the question - possibly it might be working from inside of
the clever interpreter, but what happens if one want to create the shared
library ? No smart "automatic macro compilation" will be called then.
Jacek.