Fixed private macro name issue (#1968)

docs/user_guide.md

diff --git a/docs/user_guide.md b/docs/user_guide.md
index 5fc0db9..3b8f9d5 100644
--- a/docs/user_guide.md
+++ b/docs/user_guide.md
@@ -712,7 +712,7 @@
 ```c++
 template<typename Sz>
 class SizedFixture : public benchmark::Fixture {
-  static constexpr Size = Sz::value;
+  static constexpr auto Size = Sz::value;
   int myValue;
 };
 

include/benchmark/benchmark.h

diff --git a/include/benchmark/benchmark.h b/include/benchmark/benchmark.h
index c4b5d89..188377a 100644
--- a/include/benchmark/benchmark.h
+++ b/include/benchmark/benchmark.h
@@ -1657,9 +1657,10 @@
       (::benchmark::internal::RegisterBenchmarkInternal(                      \
           ::benchmark::internal::make_unique<UniqueName>()))
 
-#define BENCHMARK_TEMPLATE_INSTANTIATE_F(BaseClass, Method, ...) \
-  BENCHMARK_TEMPLATE_PRIVATE_INSTANTIATE_F(                      \
-      BaseClass, Method, BENCHMARK_PRIVATE_NAME(tf), __VA_ARGS__)
+#define BENCHMARK_TEMPLATE_INSTANTIATE_F(BaseClass, Method, ...)    \
+  BENCHMARK_TEMPLATE_PRIVATE_INSTANTIATE_F(                         \
+      BaseClass, Method, BENCHMARK_PRIVATE_NAME(BaseClass##Method), \
+      __VA_ARGS__)
 
 // This macro will define and register a benchmark within a fixture class.
 #define BENCHMARK_F(BaseClass, Method)           \