include example of checks argument

Author: teunbrand

R/make-constructor.R

@@ -41,6 +41,21 @@ NULL
 #' p <- ggplot(mtcars, aes(disp, mpg))
 #' p + geom_test()
 #' p + geom_test(grob = grid::circleGrob())
+#'
+#' # The `checks` argument can be used to evaluate arbitrary expressions in
+#' # the constructor before building the layer.
+#' geom_path2 <- make_constructor(
+#'   GeomPath, checks = rlang::exprs(
+#'     match.arg(lineend, c("butt", "round", "square")),
+#'     match.arg(linejoin, c("round", "mitre", "bevel"))
+#'   )
+#' )
+#'
+#' # Note the inclusion of the expressions
+#' print(geom_path2)
+#'
+#' # Argument mismatch is detected
+#' try(geom_path2(linejoin = "foo"))
 make_constructor <- function(x, ...) {
   UseMethod("make_constructor")
 }