Introducing {gozer} add destruction artefacts to R objects

2021-09-28

gozer - choose the form of the destructor

gozer allows you to attach a ‘destructor’ artefact (either a string or a function) to an R object.

When the R object is destroyed (i.e. garbage collected) the ‘destructor’ artefact is printed or called.

What’s in the box

  • gozer() to attach a destructor artefact to an object.

Installation

You can install from GitHub with:

# install.package('remotes')
remotes::install_github('coolbutuseless/gozer')

Printing a string as a ‘destructor’ artefact.

library(gozer)

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Define an object and add a string destruction artefact
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a <- 'hello'
a <- gozer(a, "I was garbage collected! Goodbye ...")

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Destructor is added as object attribute as a NULL external pointer on t
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a
#> [1] "hello"
#> attr(,"destructor")
#> <pointer: 0x0>
#> attr(,"class")
#> [1] "gozer"
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Destroy the object and get the destruction artefact
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
rm(a)
invisible(gc())
#> I was garbage collected! Goodbye ...

Calling a function as a ‘destructor’ artefact.

library(gozer)

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Funciton to call when object is destroyed. 
# Argument will be an external pointer object which is unusable
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ff <- function(ext_ptr) {
  print("There was definitely a garbage collection event")
}

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Define an object and add a function as a destruction artefact
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a <- 'hello'
a <- gozer(a, ff)
a
#> [1] "hello"
#> attr(,"destructor")
#> <pointer: 0x0>
#> attr(,"class")
#> [1] "gozer"
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Destroy the object and get the destruction artefact
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
rm(a)
invisible(gc())
#> [1] "There was definitely a garbage collection event"

Acknowledgements

  • R Core for developing and maintaining the language.
  • CRAN maintainers, for patiently shepherding packages onto CRAN and maintaining the repository

Gozer the Gozerian