headless: Add a Maybe-type

headless/public/util/maybe_unittest.cc

+// Copyright 2016 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.
+
+#include "headless/public/util/maybe.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace headless {
+namespace {
+
+class MoveOnlyType {
+ public:
+  MoveOnlyType() {}
+  MoveOnlyType(MoveOnlyType&& other) {}
+
+  void operator=(MoveOnlyType&& other) {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MoveOnlyType);
+};
+
+}  // namespace
+
+TEST(MaybeTest, Nothing) {
+  Maybe<int> maybe;
+  EXPECT_TRUE(maybe.IsNothing());
+  EXPECT_FALSE(maybe.IsJust());
+}
+
+TEST(MaybeTest, Just) {
+  Maybe<int> maybe = Just(1);
+  EXPECT_FALSE(maybe.IsNothing());
+  EXPECT_TRUE(maybe.IsJust());
+  EXPECT_EQ(1, maybe.FromJust());
+
+  const Maybe<int> const_maybe = Just(2);
+  EXPECT_EQ(2, const_maybe.FromJust());
+}
+
+TEST(MaybeTest, Equality) {
+  Maybe<int> a;
+  Maybe<int> b;
+  EXPECT_EQ(a, b);
+  EXPECT_EQ(b, a);
+
+  a = Just(1);
+  EXPECT_NE(a, b);
+  EXPECT_NE(b, a);
+
+  b = Just(2);
+  EXPECT_NE(a, b);
+  EXPECT_NE(b, a);
+
+  b = Just(1);
+  EXPECT_EQ(a, b);
+  EXPECT_EQ(b, a);
+}
+
+TEST(MaybeTest, Assignment) {
+  Maybe<int> a = Just(1);
+  Maybe<int> b = Nothing<int>();
+  EXPECT_NE(a, b);
+
+  b = a;
+  EXPECT_EQ(a, b);
+}
+
+TEST(MaybeTest, MoveOnlyType) {
+  MoveOnlyType value;
+  Maybe<MoveOnlyType> a = Just(std::move(value));
+  EXPECT_TRUE(a.IsJust());
+
+  Maybe<MoveOnlyType> b = Just(MoveOnlyType());
+  EXPECT_TRUE(b.IsJust());
+
+  Maybe<MoveOnlyType> c = Nothing<MoveOnlyType>();
+  c = std::move(a);
+  EXPECT_TRUE(c.IsJust());
+
+  MoveOnlyType d = std::move(b.FromJust());
+}
+
+}  // namespace headless