operator== for ReadMostlySharedPtr to nullptr_t

Summary: add operator== against nullptr_t for ReadMostlySharedPtr

Reviewed By: andriigrynenko, nbronson, yfeldblum

Differential Revision: D4128722

fbshipit-source-id: 40d08bb85bfe2f96ad4ed4995f5829e0616d0661

folly/experimental/ReadMostlySharedPtr.h

@@ -395,4 +395,60 @@ class ReadMostlyMainPtrDeleter {
   std::vector<RefCount*> refCounts_;
   std::vector<folly::Function<void()>> decrefs_;
 };
+
+template <typename T, typename RefCount>
+inline bool operator==(
+    const ReadMostlyMainPtr<T, RefCount>& ptr,
+    std::nullptr_t) {
+  return ptr.get() == nullptr;
+}
+
+template <typename T, typename RefCount>
+inline bool operator==(
+    std::nullptr_t,
+    const ReadMostlyMainPtr<T, RefCount>& ptr) {
+  return ptr.get() == nullptr;
+}
+
+template <typename T, typename RefCount>
+inline bool operator==(
+    const ReadMostlySharedPtr<T, RefCount>& ptr,
+    std::nullptr_t) {
+  return ptr.get() == nullptr;
+}
+
+template <typename T, typename RefCount>
+inline bool operator==(
+    std::nullptr_t,
+    const ReadMostlySharedPtr<T, RefCount>& ptr) {
+  return ptr.get() == nullptr;
+}
+
+template <typename T, typename RefCount>
+inline bool operator!=(
+    const ReadMostlyMainPtr<T, RefCount>& ptr,
+    std::nullptr_t) {
+  return !(ptr == nullptr);
+}
+
+template <typename T, typename RefCount>
+inline bool operator!=(
+    std::nullptr_t,
+    const ReadMostlyMainPtr<T, RefCount>& ptr) {
+  return !(ptr == nullptr);
+}
+
+template <typename T, typename RefCount>
+inline bool operator!=(
+    const ReadMostlySharedPtr<T, RefCount>& ptr,
+    std::nullptr_t) {
+  return !(ptr == nullptr);
+}
+
+template <typename T, typename RefCount>
+inline bool operator!=(
+    std::nullptr_t,
+    const ReadMostlySharedPtr<T, RefCount>& ptr) {
+  return !(ptr == nullptr);
+}
 }

folly/experimental/test/ReadMostlySharedPtrTest.cpp

@@ -297,3 +297,40 @@ TEST_F(ReadMostlySharedPtrTest, ReadMostlyMainPtrDeleter) {
 
   EXPECT_EQ(1, useGlobalCalls);
 }
+
+TEST_F(ReadMostlySharedPtrTest, nullptr) {
+  {
+    ReadMostlyMainPtr<int, TestRefCount> nptr;
+    EXPECT_TRUE(nptr == nullptr);
+    EXPECT_TRUE(nullptr == nptr);
+    EXPECT_EQ(nptr, nullptr);
+    EXPECT_EQ(nullptr, nptr);
+    EXPECT_FALSE(nptr);
+    EXPECT_TRUE(!nptr);
+
+    ReadMostlyMainPtr<int, TestRefCount> ptr(std::make_shared<int>(42));
+    EXPECT_FALSE(ptr == nullptr);
+    EXPECT_FALSE(nullptr == ptr);
+    EXPECT_NE(ptr, nullptr);
+    EXPECT_NE(nullptr, ptr);
+    EXPECT_FALSE(!ptr);
+    EXPECT_TRUE(ptr);
+  }
+  {
+    ReadMostlySharedPtr<int, TestRefCount> nptr;
+    EXPECT_TRUE(nptr == nullptr);
+    EXPECT_TRUE(nullptr == nptr);
+    EXPECT_EQ(nptr, nullptr);
+    EXPECT_EQ(nullptr, nptr);
+    EXPECT_FALSE(nptr);
+    EXPECT_TRUE(!nptr);
+
+    ReadMostlyMainPtr<int, TestRefCount> ptr(std::make_shared<int>(42));
+    EXPECT_FALSE(ptr == nullptr);
+    EXPECT_FALSE(nullptr == ptr);
+    EXPECT_NE(ptr, nullptr);
+    EXPECT_NE(nullptr, ptr);
+    EXPECT_FALSE(!ptr);
+    EXPECT_TRUE(ptr);
+  }
+}