Add "use_length" argument to str_pad()

NEWS.md

@@ -1,5 +1,8 @@
 # stringr (development version)
 
+* `str_pad()` gains `use_length` argument to control whether to use the total code
+  point width or the number of code points as "width" of a string (#190).
+
 * `str_split_fixed()` now pads with `NA` rather than `" "` (#195).
 
 * Experimental support for display `str_view()` with ANSI escapes, which

R/pad.r

@@ -6,6 +6,8 @@
 #' @param width Minimum width of padded strings.
 #' @param side Side on which padding character is added (left, right or both).
 #' @param pad Single padding character (default is a space).
+#' @param use_length If `TRUE`, use the number of characters instead of the
+#'   total of character widths (see [stringi::stri_width]).
 #' @return A character vector.
 #' @seealso [str_trim()] to remove whitespace;
 #'   [str_trunc()] to decrease the maximum width of a string.
@@ -24,12 +26,12 @@
 #'
 #' # Longer strings are returned unchanged
 #' str_pad("hadley", 3)
-str_pad <- function(string, width, side = c("left", "right", "both"), pad = " ") {
+str_pad <- function(string, width, side = c("left", "right", "both"), pad = " ", use_length = FALSE) {
   side <- match.arg(side)
 
   switch(side,
-    left = stri_pad_left(string, width, pad = pad),
-    right = stri_pad_right(string, width, pad = pad),
-    both = stri_pad_both(string, width, pad = pad)
+    left = stri_pad_left(string, width, pad = pad, use_length = use_length),
+    right = stri_pad_right(string, width, pad = pad, use_length = use_length),
+    both = stri_pad_both(string, width, pad = pad, use_length = use_length)
   )
 }

tests/testthat/test-pad.r

@@ -16,3 +16,11 @@ test_that("directions work for simple case", {
   expect_equal(pad("left"),   "       had")
   expect_equal(pad("both"),   "   had    ")
 })
+
+test_that("padding based of length works", {
+  # \u4e2d is a 2-characters-wide Chinese character
+  pad <- function(...) str_pad("\u4e2d", ..., side = "both")
+
+  expect_equal(pad(width = 6),                    "  \u4e2d  ")
+  expect_equal(pad(width = 5, use_length = TRUE), "  \u4e2d  ")
+})