Mojo C++ bindings: add empty() for Array and Map.

BUG=None

Review URL: https://codereview.chromium.org/1776583002

Cr-Commit-Position: refs/heads/master@{#379804}

4 files changed, 43 insertions, 1 deletions

diff --git a/mojo/public/cpp/bindings/array.h b/mojo/public/cpp/bindings/array.h
index cb611c6..575ba77 100644
--- a/mojo/public/cpp/bindings/array.h
+++ b/mojo/public/cpp/bindings/array.h
@@ -88,6 +88,9 @@ class Array {
   // Indicates whether the array is null (which is distinct from empty).
   bool is_null() const { return is_null_; }
 
+  // Indicates whether the array is empty (which is distinct from null).
+  bool empty() const { return vec_.empty() && !is_null_; }
+
   // Returns a reference to the first element of the array. Calling this on a
   // null or empty array causes undefined behavior.
   ConstRefType front() const { return vec_.front(); }
diff --git a/mojo/public/cpp/bindings/map.h b/mojo/public/cpp/bindings/map.h
index 4c64d48..6d0d57d 100644
--- a/mojo/public/cpp/bindings/map.h
+++ b/mojo/public/cpp/bindings/map.h
@@ -87,9 +87,14 @@ class Map {
     return TypeConverter<U, Map>::Convert(*this);
   }
 
+  // Indicates whether the map is null (which is distinct from empty).
   bool is_null() const { return is_null_; }
 
-  // Indicates the number of keys in the map.
+  // Indicates whether the map is empty (which is distinct from null).
+  bool empty() const { return map_.empty() && !is_null_; }
+
+  // Indicates the number of keys in the map, which will be zero if the map is
+  // null.
   size_t size() const { return map_.size(); }
 
   // Inserts a key-value pair into the map. Like std::map, this does not insert
diff --git a/mojo/public/cpp/bindings/tests/array_unittest.cc b/mojo/public/cpp/bindings/tests/array_unittest.cc
index c5a227e..f4dad7c 100644
--- a/mojo/public/cpp/bindings/tests/array_unittest.cc
+++ b/mojo/public/cpp/bindings/tests/array_unittest.cc
@@ -26,6 +26,23 @@ using mojo::internal::String_Data;
 
 using ArrayTest = testing::Test;
 
+// Tests null and empty arrays.
+TEST_F(ArrayTest, NullAndEmpty) {
+  Array<char> array0;
+  EXPECT_TRUE(array0.empty());
+  EXPECT_FALSE(array0.is_null());
+  array0 = nullptr;
+  EXPECT_TRUE(array0.is_null());
+  EXPECT_FALSE(array0.empty());
+
+  Array<char> array1(nullptr);
+  EXPECT_TRUE(array1.is_null());
+  EXPECT_FALSE(array1.empty());
+  array1.SetToEmpty();
+  EXPECT_TRUE(array1.empty());
+  EXPECT_FALSE(array1.is_null());
+}
+
 // Tests that basic Array operations work.
 TEST_F(ArrayTest, Basic) {
   Array<char> array(8);
diff --git a/mojo/public/cpp/bindings/tests/map_unittest.cc b/mojo/public/cpp/bindings/tests/map_unittest.cc
index 4ccd8c0..e4d2bee 100644
--- a/mojo/public/cpp/bindings/tests/map_unittest.cc
+++ b/mojo/public/cpp/bindings/tests/map_unittest.cc
@@ -42,6 +42,23 @@ const size_t kStringIntDataSize = 4;
 
 using MapTest = testing::Test;
 
+// Tests null and empty maps.
+TEST_F(MapTest, NullAndEmpty) {
+  Map<char, char> map0;
+  EXPECT_TRUE(map0.empty());
+  EXPECT_FALSE(map0.is_null());
+  map0 = nullptr;
+  EXPECT_TRUE(map0.is_null());
+  EXPECT_FALSE(map0.empty());
+
+  Map<char, char> map1(nullptr);
+  EXPECT_TRUE(map1.is_null());
+  EXPECT_FALSE(map1.empty());
+  map1.SetToEmpty();
+  EXPECT_TRUE(map1.empty());
+  EXPECT_FALSE(map1.is_null());
+}
+
 // Tests that basic Map operations work.
 TEST_F(MapTest, InsertWorks) {
   Map<String, int> map;