R/import.R

In jmbarbone/jordan: Miscellaneous, Analytic R Kernels

#' Import
#'
#' Import a single function from a package
#'
#' @param pkg String, name of the package
#' @param fun String, fun name of the function
#' @param overwrite Logical, if TRUE and `fun` is also found in the current
#'   environment, will overwrite assignment
#' @return None, called for side effects
#' @export
#'
#' @examples
#' # assigns `add` -- test with caution
#' import("magrittr", "add")

import <- function(pkg, fun, overwrite = FALSE) {
  e <- parent.frame()
  require_namespace(pkg)

  if (!overwrite && fun %in% ls(envir = e)) {
    stop(cond_import_assigned(fun))
  }

  assign(fun, pkg %colons% fun, envir = e)
}

# conditions --------------------------------------------------------------

cond_import_assigned <- function(fun) {
  new_condition(
    sprintf(
      paste(
        "`%s` has already been assigned.",
        "Use `overwite = TRUE` to overwrite assignment."
      ),
      fun
    ),
    "import_assigned"
  )
}