R help - Jan 2010 - Problem with S4 generic function print

First, if I have an S4 class boo should I define S3 method for  
printing print.boo(..) or should I define S4 method print(..).
I mainly need to define print function only because some user might  
call it and then I would like to dispatch the call to
right function instead.

Second, it seems that by defining S4 generic function print, it is  
possible to break argument hinting on the status bar.
Namely, as I understand, the Mac OS X GUI client makes a call args()  
if something like

letter(

is typed to console. Since letter() function does not exists, it  
should return nothing to the status bar and nothing to
console, as I as a user have not entered any call, yet. However, if S4  
generic print is defined, a mysterious error
message

Error in args(letter) : no function to return from, jumping to top level

appears after typing

letter()

without return('\n') to console. It seems bizarre...

System is

Mac OS X 10.5.8 (PowerPC)
R 2.9.1 GUI 1.28 Tiger build 32-bit (5444)
R version 2.9.1 (2009-06-26)

Minimal amount of code to get the behaviour is

  if(!isGeneric("print"))
{setGeneric("print",useAsDefault=print)}

What is the underlying problem?

Sven Laur

Hi Sven --

Sven Laur wrote:
> First, if I have an S4 class boo should I define S3 method for printing
> print.boo(..) or should I define S4 method print(..).
> I mainly need to define print function only because some user might call
> it and then I would like to dispatch the call to
> right function instead.
Usually one would define a 'show' method on S4 objects; no need for
print.boo

setMethod(show, "boo", function(object) cat("Boo!\n"))

The user gets to the right place even with print(new('boo')). Can't
help
with the rest of your post.

Martin
> 
> Second, it seems that by defining S4 generic function print, it is
> possible to break argument hinting on the status bar.
> Namely, as I understand, the Mac OS X GUI client makes a call args() if
> something like
> 
> letter(
> 
> is typed to console. Since letter() function does not exists, it should
> return nothing to the status bar and nothing to
> console, as I as a user have not entered any call, yet. However, if S4
> generic print is defined, a mysterious error
> message
> 
> Error in args(letter) : no function to return from, jumping to top level
> 
> appears after typing
> 
> letter()
> 
> without return('\n') to console. It seems bizarre...
> 
> System is
> 
> Mac OS X 10.5.8 (PowerPC)
> R 2.9.1 GUI 1.28 Tiger build 32-bit (5444)
> R version 2.9.1 (2009-06-26)
> 
> Minimal amount of code to get the behaviour is
> 
>  if(!isGeneric("print"))
{setGeneric("print",useAsDefault=print)}
> 
> What is the underlying problem?
> 
> Sven Laur
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

-- 
Martin Morgan
Computational Biology / Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N.
PO Box 19024 Seattle, WA 98109

Location: Arnold Building M1 B861
Phone: (206) 667-2793