Ensure std::iterator_traits<StateIterator> instantiates.

Due to ADL lookup performed on the begin and end functions of `for (auto _ : State)`, std::iterator_traits may get incidentally instantiated. This patch ensures the library can tolerate that.

Ensure std::iterator_traits<StateIterator> instantiates.
858688b8 · Eric Fiselier · 6ecf8a8e · 858688b8 · 858688b8
Commit 858688b8 authored Feb 21, 2018 by Eric Fiselier
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benchmark.h include/benchmark/benchmark.h +1 -0

basic_test.cc test/basic_test.cc +6 -0

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--- a/include/benchmark/benchmark.h
+++ b/include/benchmark/benchmark.h
@@ -669,6 +669,7 @@ struct State::StateIterator {
  typedef Value value_type;
  typedef Value reference;
  typedef Value pointer;
+  typedef std::ptrdiff_t difference_type;

 private:
  friend class State;

--- a/test/basic_test.cc
+++ b/test/basic_test.cc
@@ -126,4 +126,10 @@ void BM_RangedFor(benchmark::State& state) {
 }
 BENCHMARK(BM_RangedFor);

+// Ensure that StateIterator provides all the necessary typedefs required to
+// instantiate std::iterator_traits.
+static_assert(std::is_same<
+  typename std::iterator_traits<benchmark::State::StateIterator>::value_type,
+  typename benchmark::State::StateIterator::value_type>::value, "");
+
 BENCHMARK_MAIN();