No partial matching in theme subsetting (#5522)

* Add dollar subsetting for themes

* add test

* Update R/theme.R

Co-authored-by: Thomas Lin Pedersen <thomasp85@gmail.com>

---------

Co-authored-by: Thomas Lin Pedersen <thomasp85@gmail.com>

Author: teunbrand

NAMESPACE

@@ -2,6 +2,7 @@
 
 S3method("$",ggproto)
 S3method("$",ggproto_parent)
+S3method("$",theme)
 S3method("$<-",uneval)
 S3method("+",gg)
 S3method("[",mapped_discrete)

R/theme.R

@@ -804,5 +804,10 @@ is.subclass <- function(x, y) {
 #' @keywords internal
 is.theme <- function(x) inherits(x, "theme")
 
+#' @export
+`$.theme` <- function(x, ...) {
+  .subset2(x, ...)
+}
+
 #' @export
 print.theme <- function(x, ...) utils::str(x)

tests/testthat/test-theme.R

@@ -1,5 +1,11 @@
 skip_on_cran() # This test suite is long-running (on cran) and is skipped
 
+test_that("dollar subsetting the theme does no partial matching", {
+  t <- theme(foobar = 12)
+  expect_null(t$foo)
+  expect_equal(t$foobar, 12)
+})
+
 test_that("modifying theme element properties with + operator works", {
 
   # Changing a "leaf node" works