[R] Redefine `[` for S3 class

[Luca Cerone]

Dear all,
I have defined my own class "myclass" using S3 class styles.
A myclass objects is just a matrix with some attribute attached.
When I subset my myclass the resulting matrix (or vector) doesn't
have the attributes attached.

I would like to redefine the `[` function for myclass objects (it has to behave
the same as the standard function but just attach the attributes to the subset).

I have tried to define the method:

`['.myclass <- function(X,... ) { etc...}

but it doesn't work ( I realized after that `[` is a .Primitive).
How can I define this method for my own class?

Thanks a lot in advance for the help,

Cheers,
Luca