Add rtc::Optional::reset

BUG=None

Review-Url: https://codereview.webrtc.org/2426473004
Cr-Commit-Position: refs/heads/master@{#14651}

webrtc/base/optional.h

@@ -132,10 +132,8 @@ class Optional final {
         new (&value_) T(m.value_);  // T's copy constructor.
         has_value_ = true;
       }
-    } else if (has_value_) {
-      value_.~T();
-      has_value_ = false;
-      PoisonValue();
+    } else {
+      reset();
     }
     return *this;
   }
@@ -152,10 +150,8 @@ class Optional final {
         new (&value_) T(std::move(m.value_));  // T's move constructor.
         has_value_ = true;
       }
-    } else if (has_value_) {
-      value_.~T();
-      has_value_ = false;
-      PoisonValue();
+    } else {
+      reset();
     }
     return *this;
   }
@@ -188,6 +184,15 @@ class Optional final {
     }
   }
 
+  // Destroy any contained value. Has no effect if we have no value.
+  void reset() {
+    if (!has_value_)
+      return;
+    value_.~T();
+    has_value_ = false;
+    PoisonValue();
+  }
+
   // Conversion to bool to test if we have a value.
   explicit operator bool() const { return has_value_; }
 

webrtc/base/optional_unittest.cc

@@ -369,6 +369,29 @@ TEST(OptionalTest, TestMoveAssignToFullFromT) {
       *log);
 }
 
+TEST(OptionalTest, TestResetEmpty) {
+  auto log = Logger::Setup();
+  {
+    Optional<Logger> x;
+    x.reset();
+  }
+  EXPECT_EQ(V(), *log);
+}
+
+TEST(OptionalTest, TestResetFull) {
+  auto log = Logger::Setup();
+  {
+    Optional<Logger> x(Logger(17));
+    log->push_back("---");
+    x.reset();
+    log->push_back("---");
+  }
+  EXPECT_EQ(
+      V("0:17. explicit constructor", "1:17. move constructor (from 0:17)",
+        "0:17. destructor", "---", "1:17. destructor", "---"),
+      *log);
+}
+
 TEST(OptionalTest, TestDereference) {
   auto log = Logger::Setup();
   {