Add %&&% operator (#1822)

Closes #1774

Author: snystrom

DESCRIPTION

@@ -46,7 +46,7 @@ Suggests:
 Enhances:
     winch
 Encoding: UTF-8
-RoxygenNote: 7.3.2
+RoxygenNote: 7.3.3
 Roxygen: list(markdown = TRUE)
 URL: https://rlang.r-lib.org, https://github.com/r-lib/rlang
 BugReports: https://github.com/r-lib/rlang/issues

NAMESPACE

@@ -97,6 +97,7 @@ S3method(summary,rlang_trace)
 S3method(summary,rlang_warning)
 export("!!!")
 export("!!")
+export("%&&%")
 export("%<~%")
 export("%@%")
 export("%@%<-")

NEWS.md

@@ -1,5 +1,7 @@
 # rlang (development version)
 
+* New `%&&%` operator that returns RHS when LHS is non-NULL (#1774, @snystrom).
+
 * C code no longer calls `memcpy()` and `memset()` on 0-length R object memory
   (#1797).
 * `is_syntactic_literal()` returns `FALSE` for objects with attributes, such as `array(1)` or `factor("x")` (#1817, @jonthegeek).

R/operators.R

@@ -19,6 +19,22 @@ if (exists("%||%", envir = baseenv())) {
   `%||%` <- get("%||%", envir = baseenv())
 }
 
+#' Default value for non-`NULL`
+#'
+#' This infix operator is the conceptual opposite of `%||%`, providing a fallback
+#' only if `x` is defined.
+#'
+#' @param x,y If `x` is NULL, will return `x`; otherwise returns `y`.
+#' @export
+#' @name op-null-continuation
+#' @seealso [op-null-default]
+#' @examples
+#' 1 %&&% 2
+#' NULL %&&% 2
+`%&&%` <- function(x, y) {
+  if (!is_null(x)) y else x
+}
+
 `%|0|%` <- function(x, y) {
   if (!length(x)) y else x
 }

_pkgdown.yml

@@ -336,5 +336,6 @@ reference:
   - subtitle: Operators
     contents:
       - "`%||%`"
+      - "`%&&%`"
       - "`%|%`"
       - "`%@%`"

man/op-null-continuation.Rd

@@ -77,3 +77,9 @@ test_that("%@% works with S4 objects (#207)", {
   expect_identical(fievel@name, "Bernard")
   expect_identical(fievel@species, "MOUSE")
 })
+
+test_that("%&&% works", {
+  expect_null(NULL %&&% 2)
+  expect_null(1 %&&% NULL)
+  expect_equal(1 %&&% 2, 2)
+})