reg.finalizer: Finalization of Objects

Description

Registers an R function to be called upon garbage collection of object or (optionally) at the end of an R session.

Usage

reg.finalizer(e, f, onexit = FALSE)

Arguments

Object to finalize. Must be an environment or an external pointer.

Function to call on finalization. Must accept a single argument, which will be the object to finalize.

onexit

logical: should the finalizer be run if the object is still uncollected at the end of the R session?

Value

NULL.

Details

The main purpose of this function is to allow objects that refer to external items (a temporary file, say) to perform cleanup actions when they are no longer referenced from within R. This only makes sense for objects that are never copied on assignment, hence the restriction to environments and external pointers.

Inter alia, it provides a way to program code to be run at the end of an R session without manipulating .Last. For use in a package, it is often a good idea to set a finalizer on an object in the namespace: then it will be called at the end of the session, or soon after the namespace is unloaded if that is done during the session.

Examples

Run this code

f <- function(e) print("cleaning....")
g <- function(x){ e <- environment(); reg.finalizer(e, f) }
g()
invisible(gc()) # trigger cleanup