Move std::chrono using statements to util/

This patch moves openscreen::<time type> using statements to be part of
a new util/ header, chrono_helpers.h. Some helpful convenience
functions are provided for doing conversions, and a new conversion
method, to_duration, is added to the Clock implementation.

Change-Id: I5a153c4da5266bceea97de0cad00a71a739f71ca
Reviewed-on: https://chromium-review.googlesource.com/c/openscreen/+/2222684
Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Reviewed-by: Ryan Keane <rwkeane@google.com>
Commit-Queue: Jordan Bayles <jophba@chromium.org>

3 files changed, 59 insertions, 6 deletions

diff --git a/util/BUILD.gn b/util/BUILD.gn
index b2100346..52f18bd8 100644
--- a/util/BUILD.gn
+++ b/util/BUILD.gn
@@ -23,6 +23,7 @@ source_set("util") {
     "alarm.h",
     "big_endian.cc",
     "big_endian.h",
+    "chrono_helpers.h",
     "crypto/certificate_utils.cc",
     "crypto/certificate_utils.h",
     "crypto/digest_sign.cc",
diff --git a/util/alarm_unittest.cc b/util/alarm_unittest.cc
index 5fad74bf..094afc9c 100644
--- a/util/alarm_unittest.cc
+++ b/util/alarm_unittest.cc
@@ -5,10 +5,12 @@
 #include "util/alarm.h"
 
 #include <algorithm>
+#include <chrono>
 
 #include "gtest/gtest.h"
 #include "platform/test/fake_clock.h"
 #include "platform/test/fake_task_runner.h"
+#include "util/chrono_helpers.h"
 
 namespace openscreen {
 namespace {
@@ -26,7 +28,7 @@ class AlarmTest : public testing::Test {
 };
 
 TEST_F(AlarmTest, RunsTaskAsClockAdvances) {
-  constexpr Clock::duration kDelay = std::chrono::milliseconds(20);
+  constexpr Clock::duration kDelay = milliseconds(20);
 
   const Clock::time_point alarm_time = FakeClock::now() + kDelay;
   Clock::time_point actual_run_time{};
@@ -61,12 +63,12 @@ TEST_F(AlarmTest, RunsTaskImmediately) {
   ASSERT_EQ(expected_run_time, actual_run_time);
 
   // Confirm the lambda is only run once.
-  clock()->Advance(std::chrono::seconds(2));
+  clock()->Advance(seconds(2));
   ASSERT_EQ(expected_run_time, actual_run_time);
 }
 
 TEST_F(AlarmTest, CancelsTaskWhenGoingOutOfScope) {
-  constexpr Clock::duration kDelay = std::chrono::milliseconds(20);
+  constexpr Clock::duration kDelay = milliseconds(20);
   constexpr Clock::time_point kNever{};
 
   Clock::time_point actual_run_time{};
@@ -85,7 +87,7 @@ TEST_F(AlarmTest, CancelsTaskWhenGoingOutOfScope) {
 }
 
 TEST_F(AlarmTest, Cancels) {
-  constexpr Clock::duration kDelay = std::chrono::milliseconds(20);
+  constexpr Clock::duration kDelay = milliseconds(20);
 
   const Clock::time_point alarm_time = FakeClock::now() + kDelay;
   Clock::time_point actual_run_time{};
@@ -104,8 +106,8 @@ TEST_F(AlarmTest, Cancels) {
 }
 
 TEST_F(AlarmTest, CancelsAndRearms) {
-  constexpr Clock::duration kShorterDelay = std::chrono::milliseconds(10);
-  constexpr Clock::duration kLongerDelay = std::chrono::milliseconds(100);
+  constexpr Clock::duration kShorterDelay = milliseconds(10);
+  constexpr Clock::duration kLongerDelay = milliseconds(100);
 
   // Run the test twice: Once when scheduling first with a long delay, then a
   // shorter delay; and once when scheduling first with a short delay, then a
diff --git a/util/chrono_helpers.h b/util/chrono_helpers.h
new file mode 100644
index 00000000..a3711bbe
--- /dev/null
+++ b/util/chrono_helpers.h
@@ -0,0 +1,50 @@
+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UTIL_CHRONO_HELPERS_H_
+#define UTIL_CHRONO_HELPERS_H_
+
+#include <chrono>
+
+// This file is a collection of helpful utilities and using statement for
+// working with std::chrono. In practice we previously defined these frequently,
+// this header allows for a single set of convenience statements.
+namespace openscreen {
+
+using hours = std::chrono::hours;
+using microseconds = std::chrono::microseconds;
+using milliseconds = std::chrono::milliseconds;
+using nanoseconds = std::chrono::nanoseconds;
+using seconds = std::chrono::seconds;
+
+// Casting statements. Note that duration_cast is not a type, it's a function,
+// so its behavior is different than the using statements above.
+template <typename D>
+static constexpr hours to_hours(D d) {
+  return std::chrono::duration_cast<hours>(d);
+}
+
+template <typename D>
+static constexpr microseconds to_microseconds(D d) {
+  return std::chrono::duration_cast<microseconds>(d);
+}
+
+template <typename D>
+static constexpr milliseconds to_milliseconds(D d) {
+  return std::chrono::duration_cast<milliseconds>(d);
+}
+
+template <typename D>
+static constexpr nanoseconds to_nanoseconds(D d) {
+  return std::chrono::duration_cast<nanoseconds>(d);
+}
+
+template <typename D>
+static constexpr seconds to_seconds(D d) {
+  return std::chrono::duration_cast<seconds>(d);
+}
+
+}  // namespace openscreen
+
+#endif  // UTIL_CHRONO_HELPERS_H_