No longer require a functor passed to ResultOf matcher to define result_of type.

This makes ResultOf more convenient to use. In particular, the matcher now accepts
lambdas.

PiperOrigin-RevId: 210118509

googlemock/test/gmock-matchers_test.cc

@@ -4597,6 +4597,7 @@ struct PolymorphicFunctor {
   typedef int result_type;
   int operator()(int n) { return n; }
   int operator()(const char* s) { return static_cast<int>(strlen(s)); }
+  std::string operator()(int *p) { return p ? "good ptr" : "null"; }
 };
 
 TEST(ResultOfTest, WorksForPolymorphicFunctors) {
@@ -4611,6 +4612,23 @@ TEST(ResultOfTest, WorksForPolymorphicFunctors) {
   EXPECT_FALSE(matcher_string.Matches("shrt"));
 }
 
+#if GTEST_LANG_CXX11
+TEST(ResultOfTest, WorksForPolymorphicFunctorsIgnoringResultType) {
+  Matcher<int*> matcher = ResultOf(PolymorphicFunctor(), "good ptr");
+
+  int n = 0;
+  EXPECT_TRUE(matcher.Matches(&n));
+  EXPECT_FALSE(matcher.Matches(nullptr));
+}
+
+TEST(ResultOfTest, WorksForLambdas) {
+  Matcher<int> matcher =
+      ResultOf([](int str_len) { return std::string(str_len, 'x'); }, "xxx");
+  EXPECT_TRUE(matcher.Matches(3));
+  EXPECT_FALSE(matcher.Matches(1));
+}
+#endif
+
 const int* ReferencingFunction(const int& n) { return &n; }
 
 struct ReferencingFunctor {