Something I have been trying to do in ROOT without any success is to write
an independent function and have it pretend to be a variable of a Tree or
NTuple in ROOT. Much like you used to be able to write a F77 method in PAW
and have it behave as a NTuple variable.
What I essentially want to be able to type on the command line is:
mytree->Draw("myfunc");
where 'myfunc' is function of the type:
double myfunc(TTree *)
I know that I could use MakeClass (for NTuples) or the base classes for a
ROOT Tree and add a method to the class. However this makes it extremely
hard to cope with updates to the code since I have to redit the class
header file to include every method prototype. It is also a big mess since
when analysing data I will write very many such functions, most of which I
probably don't care about at any one time, and so the header file fills up
with unused prototypes that I don't want to delete just in case I do want
to revisit an old method.
Failing something like this then is it at least possible, when using
trees, to make ROOT read the data as a derived class? For example if I
have a TTree with a Branch containing 'Muon' objects can I make ROOT read
those in a 'MyMuon' objects where 'MyMuon' inherits from 'Muon'?
In this way I could put my methods into 'MyMuon' and still invoke them
from the Draw command. That way when a new version of 'Muon' is released I
simply recompile my code.
I've tried to work around this problem with function pointers but the C++
interpreter doesn't like these. I've also wondered if, since the Draw
command must use the class dictionary to look up members, whether it is
possible to add a method after the fact by adding it to the dictionary
directly but this seems sufficiently hard (and may be impossible) that I
haven't tried it yet.
Any help would be appreciated,
Roger
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