some upgrades

1. move the definition of callback_function to the benchmark namespace. in order for the user to use this
2. add overloads for Stup/Teardown

Author: EfesX

include/benchmark/benchmark.h

@@ -304,6 +304,10 @@ BENCHMARK(BM_test)->Unit(benchmark::kMillisecond);
 
 namespace benchmark {
 class BenchmarkReporter;
+class State;
+
+// Define alias of Setup/Teardown callback function type
+using callback_function = std::function<void(const benchmark::State&)>;
 
 // Default number of minimum benchmark running time in seconds.
 const char kDefaultMinTimeStr[] = "0.5s";
@@ -1080,9 +1084,6 @@ class BENCHMARK_EXPORT Benchmark {
  public:
   virtual ~Benchmark();
 
-  // Define alias of Setup/Teardown callback function type
-  using callback_function = std::function<void(const benchmark::State&)>;
-
   // Note: the following methods all return "this" so that multiple
   // method calls can be chained together in one expression.
 
@@ -1164,7 +1165,9 @@ class BENCHMARK_EXPORT Benchmark {
   //
   // The callback must not be NULL or self-deleting.
   Benchmark* Setup(callback_function&&);
+  Benchmark* Setup(const callback_function&);
   Benchmark* Teardown(callback_function&&);
+  Benchmark* Teardown(const callback_function&);
 
   // Pass this benchmark object to *func, which can customize
   // the benchmark by calling various methods like Arg, Args,

src/benchmark_api_internal.h

@@ -68,7 +68,6 @@ class BenchmarkInstance {
   IterationCount iterations_;
   int threads_;  // Number of concurrent threads to us
 
-  using callback_function = Benchmark::callback_function;
   callback_function setup_ = nullptr;
   callback_function teardown_ = nullptr;
 };

src/benchmark_register.cc

@@ -343,12 +343,24 @@ Benchmark* Benchmark::Setup(callback_function&& setup) {
   return this;
 }
 
+Benchmark* Benchmark::Setup(const callback_function& setup) {
+  BM_CHECK(setup != nullptr);
+  setup_ = std::move(setup);
+  return this;
+}
+
 Benchmark* Benchmark::Teardown(callback_function&& teardown) {
   BM_CHECK(teardown != nullptr);
   teardown_ = std::forward<callback_function>(teardown);
   return this;
 }
 
+Benchmark* Benchmark::Teardown(const callback_function& teardown) {
+  BM_CHECK(teardown != nullptr);
+  teardown_ = teardown;
+  return this;
+}
+
 Benchmark* Benchmark::RangeMultiplier(int multiplier) {
   BM_CHECK(multiplier > 1);
   range_multiplier_ = multiplier;