From 858688b845b86dc43a7e23f8ec0f94a8e63bfe20 Mon Sep 17 00:00:00 2001
From: Eric Fiselier <eric@efcs.ca>
Date: Wed, 21 Feb 2018 00:54:19 -0700
Subject: [PATCH] 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.
---
 include/benchmark/benchmark.h | 1 +
 test/basic_test.cc            | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/include/benchmark/benchmark.h b/include/benchmark/benchmark.h
index 5fed767d..1eeaef64 100644
--- 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;
diff --git a/test/basic_test.cc b/test/basic_test.cc
index 12579c09..100f6898 100644
--- 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();