R/zzz.R

In paleolimbot/rlibproj: Generic Coordinate Transformation Library ('PROJ') R API

.onLoad <- function(...) {
  # load the libproj function pointers here
  requireNamespace("libproj", quietly = TRUE)
  .Call(rproj_c_init)

  # try to assign the default context
  proj_context_env$ctx <- try(proj_context_create())

  # regsiter methods
  s3_register("sf::st_crs", "rproj_proj")
}

s3_register <- function(generic, class, method = NULL) {
  stopifnot(is.character(generic), length(generic) == 1)
  stopifnot(is.character(class), length(class) == 1)

  pieces <- strsplit(generic, "::")[[1]]
  stopifnot(length(pieces) == 2)
  package <- pieces[[1]]
  generic <- pieces[[2]]

  caller <- parent.frame()

  get_method_env <- function() {
    top <- topenv(caller)
    if (isNamespace(top)) {
      asNamespace(environmentName(top))
    } else {
      caller
    }
  }
  get_method <- function(method, env) {
    if (is.null(method)) {
      get(paste0(generic, ".", class), envir = get_method_env())
    } else {
      method
    }
  }

  register <- function(...) {
    envir <- asNamespace(package)

    # Refresh the method each time, it might have been updated by
    # `devtools::load_all()`
    method_fn <- get_method(method)
    stopifnot(is.function(method_fn))


    # Only register if generic can be accessed
    if (exists(generic, envir)) {
      registerS3method(generic, class, method_fn, envir = envir)
    } else if (identical(Sys.getenv("NOT_CRAN"), "true")) {
      warning(sprintf(
        "Can't find generic `%s` in package %s to register S3 method.",
        generic,
        package
      ))
    }
  }

  # Always register hook in case package is later unloaded & reloaded
  setHook(packageEvent(package, "onLoad"), register)

  # Avoid registration failures during loading (pkgload or regular)
  if (isNamespaceLoaded(package)) {
    register()
  }

  invisible()
}