On 11/19/2012 04:21 PM, Andrea Spano wrote:
Hello the list,
As a simple example:
rm(list = ls())> setClass("tre", representation(x="numeric"))> setMethod("show", "tre", def = function(object) cat(object@x))[1] "show">
setMethod("summary", "tre", def = function(object) cat("This is a tre of value ", object@x, "\n"))Creating a generic function for ‘summary’ from package ‘base’
in the global environment[1] "summary"> ls()[1] "summary"
R copies generic summary into the current environment.
I understand it as: If you want R to create a specific "summary"
method for objects of class "tre" R needs the generic method in the
same environment (R_GloabalEnv).
In fact, summary is listed by ls in in my local env.
Why R does not do the same with generic method "show"?
I know that generic method "show" is from package "methods" while
summary is package "base". Does it matter somehow?
There are several object systems in R. Your use of setMethod indicates that you
are creating an S4 method, to be associated with an S4 generic. 'show' is a
generic in the S4 object system, and setMethod(show, <...>) associates your
method with this generic. 'summary' is a generic in the S3 object system.
setMethod(summary, <...>) realizes that there is not yet an S4 generic summary,
so creates an S4 generic (with the S3 generic as the default method) and then
adds your method to the newly created S4 generic. The S3 generic is not copied
to the global environment.
Martin
Can anyone point me to the right reference?
Thanks in advance for your help ...
Andrea
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