R devel - Oct 2006 - Overloading functions

Hi Everyone

I have a function f which does something using a function g.  Function f  
is in a library and g has a default stub in the library but will be mainly  
overloaded in a later R script.  For example:

########## In a compiled package 'P' #################
g <- function() {
    cat("Original function g");
}

f <- function( newGsource=NULL ) {
     if( is.null(newGsource) == FALSE ) {
	source( newGsource ); # load new function g
     }	
     g();
     return(1);
}
#####################################################

If I call f() then I get "Original function g".

But I want to overload g so I do the following in the file newg.R:

############### CONTENTS of newg.R ##########################
g <- function() {
    cat("New function g in newg.R");
}
################ END CONTENTS ###############################

and call f( newGsource="newg.R" ) but I still get "Original
function g".

Any suggestions?

Tom

-- 
---

Tom McCallum

WWW: http://www.tom-mccallum.com
Tel: 0131-4783393
Mobile: 07866-470257

On Fri, 27 Oct 2006 14:49:15 +0100, Paul Roebuck <roebuck at
mdanderson.org>
wrote:
> On Fri, 27 Oct 2006, Tom McCallum wrote:
>
>> I have a function f which does something using a function g.  Function
f
>> is in a library and g has a default stub in the library but will be  
>> mainly
>> overloaded in a later R script.  For example:
>>
>> ########## In a compiled package 'P' #################
>> g <- function() {
>>     cat("Original function g");
>> }
>>
>> f <- function( newGsource=NULL ) {
>>      if( is.null(newGsource) == FALSE ) {
>> 	source( newGsource ); # load new function g
>>      }
>>      g();
>>      return(1);
>> }
>> #####################################################
>>
>> If I call f() then I get "Original function g".
>>
>> But I want to overload g so I do the following in the file newg.R:
>>
>> ############### CONTENTS of newg.R ##########################
>> g <- function() {
>>     cat("New function g in newg.R");
>> }
>> ################ END CONTENTS ###############################
>>
>> and call f( newGsource="newg.R" ) but I still get
"Original function g".
>>
>> Any suggestions?
>
> ?environment
>
> ----------------------------------------------------------
> SIGSIG -- signature too long (core dumped)
>
>
Thanks for that, have almost figured out how to do it,  have got my  
namespace but when I "assign" the new value
I get "cannot change value of a locked binding".  Is there any way to
say
that a particular item in a package
is able to be overridden using assign?

I assume when I export a function in the NAMESPACE file it is locking the  
value to the name.  So I assume it is here I need
to change something - if this is even possible to do.

Cheers

Tom

-- 
---

Tom McCallum