Export is_bool()

Closes #695

NAMESPACE

@@ -265,6 +265,7 @@ export(is_bare_raw)
 export(is_bare_string)
 export(is_bare_vector)
 export(is_binary_lang)
+export(is_bool)
 export(is_box)
 export(is_bytes)
 export(is_call)

NEWS.md

@@ -1,6 +1,11 @@
 
 # rlang 0.3.99.9000
 
+* `is_bool()` is a scalar type predicate that checks whether its input
+  is a single `TRUE` or `FALSE`. Like `is_string()`, it returns
+  `FALSE` when the input is missing. This is useful for type-checking
+  function arguments (#695).
+
 * Lists of quosures now have pillar methods for display in tibbles.
 
 * The performance of `exec()` has been improved. It is now on the same

R/types.R

@@ -101,8 +101,16 @@ is_null <- function(x) {
 
 #' Scalar type predicates
 #'
+#' @description
+#'
 #' These predicates check for a given type and whether the vector is
 #' "scalar", that is, of length 1.
+#'
+#' In addition to the length check, `is_string()` and `is_bool()`
+#' return `FALSE` if their input is missing. This is useful for
+#' type-checking arguments, when your function expects a single string
+#' or a single `TRUE` or `FALSE`.
+#'
 #' @inheritParams type-predicates
 #' @param x object to be tested.
 #' @seealso [type-predicates], [bare-type-predicates]
@@ -162,7 +170,8 @@ is_string <- function(x, string = NULL) {
 #' @export
 #' @rdname scalar-type-predicates
 is_scalar_bytes <- is_scalar_raw
-
+#' @export
+#' @rdname scalar-type-predicates
 is_bool <- function(x) {
   is_logical(x, n = 1) && !is.na(x)
 }

tests/testthat/test-types.R

@@ -166,3 +166,10 @@ test_that("is_string() matches on string", {
   expect_true(is_string("foo", c("bar", "foo")))
   expect_false(is_string("foo", c("bar", "baz")))
 })
+
+test_that("is_bool() checks for single `TRUE` or `FALSE`", {
+  expect_true(is_bool(TRUE))
+  expect_true(is_bool(FALSE))
+  expect_false(is_bool(NA))
+  expect_false(is_bool(c(TRUE, FALSE)))
+})