Rename argument of detect functions to .f

So they are documented with the right semantics. Closes tidyverse#348

NEWS.md

@@ -139,6 +139,10 @@ of `[<-`.  `modify.default()` is thus a shorthand for `x[] <- map(x, f)`.
 * `transpose()` now matches by name if available (#164). You can
   override the default choice with the new `.names` argument.
 
+* The function argument of `detect()` and `detect_index()` have been
+  renamed from `.p` to `.f`. This is because they have mapper
+  semantics rather than predicate semantics.
+
 
 # purrr 0.2.2.1
 

R/find-position.R

@@ -18,22 +18,42 @@
 #'
 #' 3:10 %>% detect(is_even, .right = TRUE)
 #' 3:10 %>% detect_index(is_even, .right = TRUE)
-detect <- function(.x, .p, ..., .right = FALSE) {
-  .p <- as_mapper(.p, ...)
+#'
+#'
+#' # Since `.f` is passed to as_mapper(), you can supply a
+#' # lambda-formula or a pluck object:
+#' x <- list(
+#'   list(1, foo = FALSE),
+#'   list(2, foo = TRUE),
+#'   list(3, foo = TRUE)
+#' )
+#'
+#' detect(x, "foo")
+#' detect_index(x, "foo")
+detect <- function(.x, .f, ..., .right = FALSE, .p) {
+  if (!missing(.p)) {
+    warn("`.p` has been renamed to `.f`", "purrr_2.2.3")
+    .f <- .p
+  }
+  .f <- as_mapper(.f, ...)
 
   for (i in index(.x, .right)) {
-    if (is_true(.p(.x[[i]], ...))) return(.x[[i]])
+    if (is_true(.f(.x[[i]], ...))) return(.x[[i]])
   }
   NULL
 }
 
 #' @export
 #' @rdname detect
-detect_index <- function(.x, .p, ..., .right = FALSE) {
-  .p <- as_mapper(.p, ...)
+detect_index <- function(.x, .f, ..., .right = FALSE, .p) {
+  if (!missing(.p)) {
+    warn("`.p` has been renamed to `.f`", "purrr_2.2.3")
+    .f <- .p
+  }
+  .f <- as_mapper(.f, ...)
 
   for (i in index(.x, .right)) {
-    if (is_true(.p(.x[[i]], ...))) return(i)
+    if (is_true(.f(.x[[i]], ...))) return(i)
   }
   0L
 }

tests/testthat/test-find-position.R

@@ -22,3 +22,13 @@ test_that("has_element checks whether a list contains an object", {
   expect_true(has_element(list(1, 2), 1))
   expect_false(has_element(list(1, 2), 3))
 })
+
+test_that("detect functions still work with `.p`", {
+  is_even <- function(x) x %% 2 == 0
+  expect_warning(regex = "renamed to `.f`",
+    expect_identical(detect(1:3, .p = is_even), 2L)
+  )
+  expect_warning(regex = "renamed to `.f`",
+    expect_identical(detect_index(1:3, .p = is_even), 2L)
+  )
+})