[help] Best way to extend options in targets?

[Aariq]

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Description

With geotargets, we'd like to be able to set options that ultimately get passed to write functions and we'd ideally like to use the same API as targets with tar_options_set() and tar_options_get() just for consistency and familiarity for users. In playing around, I've realized that options set with options() don't get passed to crew workers and that we probably need something more sophisticated, but how options work with targets are a bit obscure to me. Any tips or ideas for creating geotargets_options_set() and geotargets_options_get() functions?

[wlandau]

8ab2305 now implements tar_resources_custom_format() which allows you to send custom environment variables to the functions you define in tar_format(). These environment variables reach parallel workers. @noamross, this might be useful for #1232.

I think this approach is appropriate when those settings do not invalidate previous work. In other words, if the right decision is to rerun the target when a setting changes, it would be preferable to avoid tar_resources_custom_format() and instead bake the setting's value into the body of a read or write function.

Anyway, here is an example where it is fine to use tar_resources_custom_format(). No matter what serialization method you choose, readRDS() can still read the file.

library(targets)
tar_option_set(
  controller = crew::crew_controller_local()
)
tar_target(
  name = target_name,
  command = data.frame(x = 1),
  format = tar_format(
    read = function(path) {
      readRDS(file = path)
    },
    write = function(object, path) {
      version <- as.integer(Sys.getenv("SERIALIZATION", unset = ""))
      saveRDS(object = object, file = path, version = version)
    }
  ),
  resources = tar_resources(
    custom_format = tar_resources_custom_format(
      envvars = c(SERIALIZATION = "3")
    )
  )
)

[Aariq]

Thanks! This is great and simplifies things a lot for geotargets.