1 files changed, 21 insertions, 6 deletions

diff --git a/include/gtest/gtest.h b/include/gtest/gtest.h
index 6ce58d72..f7ed948b 100644
--- a/include/gtest/gtest.h
+++ b/include/gtest/gtest.h
@@ -1589,9 +1589,13 @@ class GTEST_API_ AssertHelper {
 }  // namespace internal
 
 #if GTEST_HAS_PARAM_TEST
-// The abstract base class that all value-parameterized tests inherit from.
+// The pure interface class that all value-parameterized tests inherit from.
+// A value-parameterized class must inherit from both ::testing::Test and
+// ::testing::WithParamInterface. In most cases that just means inheriting
+// from ::testing::TestWithParam, but more complicated test hierarchies
+// may need to inherit from Test and WithParamInterface at different levels.
 //
-// This class adds support for accessing the test parameter value via
+// This interface has support for accessing the test parameter value via
 // the GetParam() method.
 //
 // Use it with one of the parameter generator defining functions, like Range(),
@@ -1620,12 +1624,16 @@ class GTEST_API_ AssertHelper {
 // INSTANTIATE_TEST_CASE_P(OneToTenRange, FooTest, ::testing::Range(1, 10));
 
 template <typename T>
-class TestWithParam : public Test {
+class WithParamInterface {
  public:
   typedef T ParamType;
+  virtual ~WithParamInterface() {}
 
   // The current parameter value. Is also available in the test fixture's
-  // constructor.
+  // constructor. This member function is non-static, even though it only
+  // references static data, to reduce the opportunity for incorrect uses
+  // like writing 'WithParamInterface<bool>::GetParam()' for a test that
+  // uses a fixture whose parameter type is int.
   const ParamType& GetParam() const { return *parameter_; }
 
  private:
@@ -1638,12 +1646,19 @@ class TestWithParam : public Test {
   // Static value used for accessing parameter during a test lifetime.
   static const ParamType* parameter_;
 
-  // TestClass must be a subclass of TestWithParam<T>.
+  // TestClass must be a subclass of WithParamInterface<T> and Test.
   template <class TestClass> friend class internal::ParameterizedTestFactory;
 };
 
 template <typename T>
-const T* TestWithParam<T>::parameter_ = NULL;
+const T* WithParamInterface<T>::parameter_ = NULL;
+
+// Most value-parameterized classes can ignore the existence of
+// WithParamInterface, and can just inherit from ::testing::TestWithParam.
+
+template <typename T>
+class TestWithParam : public Test, public WithParamInterface<T> {
+};
 
 #endif  // GTEST_HAS_PARAM_TEST