Hopefully fixes error when ggplot2 is not loaded

ref #21

DESCRIPTION

@@ -14,5 +14,7 @@ LazyData: true
 Imports:
   ggplot2 (>= 3.0.0),
   stringi
-RoxygenNote: 6.1.1
+RoxygenNote: 7.0.2
 Roxygen: list(markdown = TRUE)
+Suggests: 
+    testthat

NAMESPACE

@@ -6,3 +6,6 @@ export(new_scale_color)
 export(new_scale_colour)
 export(new_scale_fill)
 importFrom(ggplot2,ggplot_add)
+importFrom(ggplot2,guide_colorbar)
+importFrom(ggplot2,guide_colourbar)
+importFrom(ggplot2,guide_legend)

NEWS.md

@@ -1,3 +1,9 @@
+# 0.5.9000
+
+## Bugfixes
+
+* Fixed error when adding a scale with `ggplot2` not loaded. (#21, thanks @rmendels)
+
 # 0.4.0 - G minor
 
 ## Bugfixes

R/new-scale.R

@@ -143,6 +143,7 @@ bump_aes_scales <- function(scales, new_aes) {
   lapply(scales, bump_aes_scale, new_aes = new_aes)
 }
 
+#' @importFrom ggplot2 guide_colourbar guide_colorbar guide_legend
 bump_aes_scale <- function(scale, new_aes) {
   old_aes <- scale$aesthetics[remove_new(scale$aesthetics) %in% new_aes]
   if (length(old_aes) != 0) {
@@ -153,8 +154,7 @@ bump_aes_scale <- function(scale, new_aes) {
     no_guide <- isFALSE(scale$guide) | isTRUE(scale$guide == "none")
     if (!no_guide) {
       if (is.character(scale$guide)) {
-
-        scale$guide <- match.fun(paste("guide_", scale$guide, sep = ""))()
+        scale$guide <- get(paste0("guide_", scale$guide), mode = "function")()
       }
       scale$guide$available_aes[scale$guide$available_aes %in% old_aes] <- new_aes
     }

tests/testthat.R

@@ -0,0 +1,4 @@
+library(testthat)
+library(ggnewscale)
+
+test_check("ggnewscale")

tests/testthat/test-newscale.R

@@ -0,0 +1,15 @@
+
+
+topography <- expand.grid(x = 1:nrow(volcano),
+                          y = 1:ncol(volcano))
+topography$z <- c(volcano)
+
+test_that("works when ggplot2 not loaded", {
+
+  g <- ggplot2::ggplot(mapping = ggplot2::aes(x, y)) +
+    ggplot2::geom_contour(data = topography, ggplot2::aes(z = z, color = ..level..)) +
+    new_scale_color()
+
+  expect_true(inherits(g,"ggplot"))
+
+})