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Add Function

Source: vignettes/golem-add-function.Rmd
golem-add-function.Rmd

Add Function

You are helping a user add functions to their golem Shiny application.

Creating Functions

Use the appropriate golem::add_*() function based on where the code belongs:

  • golem::add_fct("name", with_test = TRUE) - Business logic and factory functions
  • golem::add_utils("name", with_test = TRUE) - Utility functions

Function Types

Factory Functions (R/fct_*.R)

  • Contain business logic that can be reused
  • Should be testable in isolation, outside of Shiny context
  • Example: data processing, calculations, validations
  • Created with golem::add_fct()

Utility Functions (R/utils_*.R)

  • General-purpose helpers
  • Reusable across modules
  • Can be utility functions for modules: R/mod_<name>_utils_<fn>.R
  • Created with golem::add_utils()

Documentation

All functions MUST be documented with roxygen2. In almost all cases, the internal functions do no need to be exported. They are only useful inside the app. If ever you have a doubt, ask the user.

#' Function Title
#'
#' Function description
#'
#' @param x Parameter description
#'
#' @return What the function returns
#'
#' @examples
#' my_func(x = 1)
#'
#' @importFrom pkg_name func_name
#'
#' @export
my_func <- function(x) {
  # function body
}

Important Rules

  • Run devtools::document() after adding roxygen comments
  • All functions must have @examples
  • Use @importFrom for external package functions
  • Use @noRd for internal functions (don’t document in Rd files)
  • Never use library(), require(), or source() inside functions
  • Use @inheritParams to avoid duplicating parameter docs

Testing

  • Tests should be hermetic - each test_that() block sets up its own data
  • Test business logic outside of Shiny context when possible
  • Use withr::local_*() for temporary state changes
  • Write temporary files only to withr::local_tempfile() or withr::local_tempdir()
  • Store static test data in tests/testthat/fixtures/

Code Quality

  • Follow the tidyverse style guide
  • Use air format . if installed
  • No non-ASCII characters in R/ files (or create tools/check.env with _R_CHECK_ASCII_CODE_=FALSE)
  • Use TRUE/FALSE, never T/F
  • Never use = for assignment, use <-
  • Avoid modifying global state - use on.exit(..., add = TRUE) if necessary