Merge pull request #50 from rstudio/wch-fix-promise-all-null

Fix NULL handling in promise_all()

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: promises
 Type: Package
 Title: Abstractions for Promise-Based Asynchronous Programming
-Version: 1.0.1.9000
+Version: 1.0.1.9001
 Authors@R: c(
       person("Joe", "Cheng", email = "joe@rstudio.com", role = c("aut", "cre")),
       person("RStudio", role = c("cph", "fnd"))

NEWS.md

@@ -1,4 +1,9 @@
+promises 1.0.1.9001
+================
+
+* Fixed [#49](https://github.com/rstudio/promises/issues/49): `promise_all()` previously did not handle `NULL` values correctly. ([#50](https://github.com/rstudio/promises/pull/50))
+
 promises 1.0.1
 ================
 
-- Initial CRAN release
+* Initial CRAN release

R/utils.R

@@ -69,7 +69,9 @@ promise_all <- function(..., .list = NULL) {
       then(.list[[key]],
         onFulfilled = function(value) {
           # Save the result so we can return it to the user.
-          results[[key]] <<- value
+          # This weird assignment is similar to `results[[key]] <- value`, except
+          # that it handles NULL values correctly.
+          results[key] <<- list(value)
 
           # Record the fact that the promise was completed.
           done[[key]] <<- TRUE

tests/testthat/test-combining.R

@@ -11,4 +11,14 @@ describe("promise_all", {
     x <- promise_all(.list = list(a=a, b=b, c=c))
     expect_identical(extract(x), list(a=1, b=2, c=3))
   })
+
+  it("Handles NULLs correctly", {
+    x <- promise_all(promise_resolve(NULL), promise_resolve(NULL),
+                     promise_resolve(NULL))
+    expect_identical(extract(x), list(NULL, NULL, NULL))
+
+    x <- promise_all(a = promise_resolve(NULL), b = promise_resolve(NULL),
+                     c = promise_resolve(NULL))
+    expect_identical(extract(x), list(a = NULL, b = NULL, c = NULL))
+  })
 })