Functions that write functions in R packages

Not sure what the setup is here but if the objects are
intended to be proto objects then the accessor functions
could be placed in the object itself (or in an ancestor object)
rather than in the global environment.  For example, this inserts
a function get.v(.) into proto object p for each variable v in p.

library(proto)

make.accessors <- function(p, ...) {
   lapply(ls(p, ...), f. <- function(v) {
        nm <- paste("get", v, sep = ".")
        p[[nm]] <- function(.) {}
        body(p[[nm]]) <- substitute(.$v, list(v = v))
        environment(p[[nm]]) <- p
   })
   invisible(p)
}
make.accessors(p)
p$get.x()
p$get.y()

# or the constructor of objects like p could build it right it
# at object construction time
make.p <- function(...) make.accessors(proto(...))
q <- make.p(x = 1, y = 2)
q$get.x()
q$get.y()


On 2/23/07, hadley wickham <h.wickham at gmail.com> wrote:

Dear all,

Another question related to my ggplot package:  I have made some
substantial changes to the backend of my package so that plot objects
can now describe themselves much better.  A consequence of this is
that a number of convenience functions that previously I wrote by
hand, can now be written automatically.  What is the best practice for
creating these functions for bundling in a package?  I see three
possible solutions:

 * dump function specifications out to a .r file
 * dynamically create at package build time so they are including in
the package rdata file
 * dynamically create at package load time

Can anyone offer any advice as to which is preferable? (or if there's
a better way I haven't thought of)

My code currently looks like this (experimenting with two ways of
creating the functions)

create_accessors <- function(objects, name, short=NULL) {
       lapply(objects, function(x) {
               assign(paste(name, x$objname, sep="_"), x$new, pos=globalenv())
               if (!is.null(short)) {
                       eval(
                               substitute(
                                       f <- function(plot, ...) plot + add(...),
                                       list(
                                               add = as.name(paste(name, x$objname, sep="_")),
                                               f = as.name(paste(short, x$objname, sep=""))
                                       )
                               ), envir = globalenv()
                       )

               }
       })
}

Thanks,

Hadley