[R] learning S4

[cgenolin at u-paris10.fr]

Hi the list.

I try to learn the S4 programming. I find the wiki and several doc. But 
I still have few questions...

1. To define 'representation', we can use two syntax :
    - representation=list(temps = 'numeric',traj = 'matrix')
    - representation(temps = 'numeric',traj = 'matrix')
   Is there any difference ?
2. 'validityMethod' check the intialisation of a new object, but not 
the latter
   modifications. Is it possible to set up a validation that check every
   modifications ?
3. When we use setMethod('initialize',...) does the validityMethod 
become un-used ?
4. Is it possible to set up several initialization processes ?   One 
that build an objet from a data.frame, one from a matrix...

Thanks

Christophe

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