Improve the performance of as_mapper() (#899)

Fixes #820

NEWS.md

@@ -30,6 +30,9 @@
 
 ## Features and fixes
 
+* `as_mapper()` is now around twice as fast when used with character,
+  integer, or list (#820).
+
 * `vec_depth()` is now `pluck_depth()` and works with more types of input
   (#818).
 

R/as_mapper.R

@@ -98,11 +98,12 @@ find_extract_default <- function(.null, .default) {
 
 plucker <- function(i, default) {
   x <- NULL # supress global variables check NOTE
+  i <- as.list(i)
 
+  # Use metaprogramming to create function that prints nicely
   new_function(
     exprs(x = , ... = ),
-    expr(pluck(x, !!!i, .default = !!default)),
-    env = caller_env()
+    expr(pluck_raw(x, !!i, .default = !!default))
   )
 }
 

R/pluck.R

@@ -122,15 +122,19 @@
 #' @export
 pluck <- function(.x, ..., .default = NULL) {
   check_dots_unnamed()
+  pluck_raw(.x, list2(...), .default = .default)
+}
 
+pluck_raw <- function(.x, index, .default = NULL) {
   .Call(
     pluck_impl,
     x = .x,
-    index = list2(...),
+    index = index,
     missing = .default,
     strict = FALSE
   )
 }
+
 #' @rdname pluck
 #' @export
 chuck <- function(.x, ...) {