rtc_base/strong_alias_unittest.cc - src - Git at Google

 /*
  *  Copyright 2019 The Chromium Authors. All rights reserved.
  *  Copyright (c) 2021 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 #include "rtc_base/strong_alias.h"

 #include <cstdint>
 #include <map>
 #include <memory>
 #include <string>
 #include <type_traits>
 #include <utility>

 #include "rtc_base/containers/flat_map.h"
 #include "rtc_base/gunit.h"
 #include "test/gmock.h"

 // This is a copy of
 // https://source.chromium.org/chromium/chromium/src/+/main:base/types/strong_alias_unittest.cc
 // but adapted to use WebRTC's includes, remove unit tests that test the ostream
 // operator (it's removed in this port) and other adaptations to pass lint.

 namespace webrtc {
 namespace {

 // For test correctnenss, it's important that these getters return lexically
 // incrementing values as `index` grows.
 template <typename T>
 T GetExampleValue(int index);

 template <>
 int GetExampleValue<int>(int index) {
   return 5 + index;
 }
 template <>
 uint64_t GetExampleValue<uint64_t>(int index) {
   return 500U + index;
 }

 template <>
 std::string GetExampleValue<std::string>(int index) {
   return std::string('a', index);
 }

 }  // namespace

 template <typename T>
 class StrongAliasTest : public ::testing::Test {};

 using TestedTypes = ::testing::Types<int, uint64_t, std::string>;
 TYPED_TEST_SUITE(StrongAliasTest, TestedTypes);

 TYPED_TEST(StrongAliasTest, ValueAccessesUnderlyingValue) {
   using FooAlias = StrongAlias<class FooTag, TypeParam>;

   // Const value getter.
   const FooAlias const_alias(GetExampleValue<TypeParam>(1));
   EXPECT_EQ(GetExampleValue<TypeParam>(1), const_alias.value());
   static_assert(std::is_const<typename std::remove_reference<decltype(
                     const_alias.value())>::type>::value,
                 "Reference returned by const value getter should be const.");
 }

 TYPED_TEST(StrongAliasTest, ExplicitConversionToUnderlyingValue) {
   using FooAlias = StrongAlias<class FooTag, TypeParam>;

   const FooAlias const_alias(GetExampleValue<TypeParam>(1));
   EXPECT_EQ(GetExampleValue<TypeParam>(1), static_cast<TypeParam>(const_alias));
 }

 TYPED_TEST(StrongAliasTest, CanBeCopyConstructed) {
   using FooAlias = StrongAlias<class FooTag, TypeParam>;
   FooAlias alias(GetExampleValue<TypeParam>(0));
   FooAlias copy_constructed = alias;
   EXPECT_EQ(copy_constructed, alias);

   FooAlias copy_assigned;
   copy_assigned = alias;
   EXPECT_EQ(copy_assigned, alias);
 }

 TYPED_TEST(StrongAliasTest, CanBeMoveConstructed) {
   using FooAlias = StrongAlias<class FooTag, TypeParam>;
   FooAlias alias(GetExampleValue<TypeParam>(0));
   FooAlias move_constructed = std::move(alias);
   EXPECT_EQ(move_constructed, FooAlias(GetExampleValue<TypeParam>(0)));

   FooAlias alias2(GetExampleValue<TypeParam>(2));
   FooAlias move_assigned;
   move_assigned = std::move(alias2);
   EXPECT_EQ(move_assigned, FooAlias(GetExampleValue<TypeParam>(2)));

   // Check that FooAlias is nothrow move constructible. This matters for
   // performance when used in std::vectors.
   static_assert(std::is_nothrow_move_constructible<FooAlias>::value,
                 "Error: Alias is not nothow move constructible");
 }

 TYPED_TEST(StrongAliasTest, CanBeConstructedFromMoveOnlyType) {
   // Note, using a move-only unique_ptr to T:
   using FooAlias = StrongAlias<class FooTag, std::unique_ptr<TypeParam>>;

   FooAlias a(std::make_unique<TypeParam>(GetExampleValue<TypeParam>(0)));
   EXPECT_EQ(*a.value(), GetExampleValue<TypeParam>(0));

   auto bare_value = std::make_unique<TypeParam>(GetExampleValue<TypeParam>(1));
   FooAlias b(std::move(bare_value));
   EXPECT_EQ(*b.value(), GetExampleValue<TypeParam>(1));
 }

 TYPED_TEST(StrongAliasTest, MutableOperatorArrow) {
   // Note, using a move-only unique_ptr to T:
   using Ptr = std::unique_ptr<TypeParam>;
   using FooAlias = StrongAlias<class FooTag, Ptr>;

   FooAlias a(std::make_unique<TypeParam>());
   EXPECT_TRUE(a.value());

   // Check that `a` can be modified through the use of operator->.
   a->reset();

   EXPECT_FALSE(a.value());
 }

 TYPED_TEST(StrongAliasTest, MutableOperatorStar) {
   // Note, using a move-only unique_ptr to T:
   using Ptr = std::unique_ptr<TypeParam>;
   using FooAlias = StrongAlias<class FooTag, Ptr>;

   FooAlias a(std::make_unique<TypeParam>());
   FooAlias b(std::make_unique<TypeParam>());
   EXPECT_TRUE(*a);
   EXPECT_TRUE(*b);

   // Check that both the mutable l-value and r-value overloads work and we can
   // move out of the aliases.
   { Ptr ignore(*std::move(a)); }
   { Ptr ignore(std::move(*b)); }

   EXPECT_FALSE(a.value());
   EXPECT_FALSE(b.value());
 }

 TYPED_TEST(StrongAliasTest, MutableValue) {
   // Note, using a move-only unique_ptr to T:
   using Ptr = std::unique_ptr<TypeParam>;
   using FooAlias = StrongAlias<class FooTag, Ptr>;

   FooAlias a(std::make_unique<TypeParam>());
   FooAlias b(std::make_unique<TypeParam>());
   EXPECT_TRUE(a.value());
   EXPECT_TRUE(b.value());

   // Check that both the mutable l-value and r-value overloads work and we can
   // move out of the aliases.
   { Ptr ignore(std::move(a).value()); }
   { Ptr ignore(std::move(b.value())); }

   EXPECT_FALSE(a.value());
   EXPECT_FALSE(b.value());
 }

 TYPED_TEST(StrongAliasTest, SizeSameAsUnderlyingType) {
   using FooAlias = StrongAlias<class FooTag, TypeParam>;
   static_assert(sizeof(FooAlias) == sizeof(TypeParam),
                 "StrongAlias should be as large as the underlying type.");
 }

 TYPED_TEST(StrongAliasTest, IsDefaultConstructible) {
   using FooAlias = StrongAlias<class FooTag, TypeParam>;
   static_assert(std::is_default_constructible<FooAlias>::value,
                 "Should be possible to default-construct a StrongAlias.");
   static_assert(
       std::is_trivially_default_constructible<FooAlias>::value ==
           std::is_trivially_default_constructible<TypeParam>::value,
       "Should be possible to trivially default-construct a StrongAlias iff the "
       "underlying type is trivially default constructible.");
 }

 TEST(StrongAliasTest, TrivialTypeAliasIsStandardLayout) {
   using FooAlias = StrongAlias<class FooTag, int>;
   static_assert(std::is_standard_layout<FooAlias>::value,
                 "int-based alias should have standard layout. ");
   static_assert(std::is_trivially_copyable<FooAlias>::value,
                 "int-based alias should be trivially copyable. ");
 }

 TYPED_TEST(StrongAliasTest, CannotBeCreatedFromDifferentAlias) {
   using FooAlias = StrongAlias<class FooTag, TypeParam>;
   using BarAlias = StrongAlias<class BarTag, TypeParam>;
   static_assert(!std::is_constructible<FooAlias, BarAlias>::value,
                 "Should be impossible to construct FooAlias from a BarAlias.");
   static_assert(!std::is_convertible<BarAlias, FooAlias>::value,
                 "Should be impossible to convert a BarAlias into FooAlias.");
 }

 TYPED_TEST(StrongAliasTest, CannotBeImplicitlyConverterToUnderlyingValue) {
   using FooAlias = StrongAlias<class FooTag, TypeParam>;
   static_assert(!std::is_convertible<FooAlias, TypeParam>::value,
                 "Should be impossible to implicitly convert a StrongAlias into "
                 "an underlying type.");
 }

 TYPED_TEST(StrongAliasTest, ComparesEqualToSameValue) {
   using FooAlias = StrongAlias<class FooTag, TypeParam>;
   // Comparison to self:
   const FooAlias a = FooAlias(GetExampleValue<TypeParam>(0));
   EXPECT_EQ(a, a);
   EXPECT_FALSE(a != a);
   EXPECT_TRUE(a >= a);
   EXPECT_TRUE(a <= a);
   EXPECT_FALSE(a > a);
   EXPECT_FALSE(a < a);
   // Comparison to other equal object:
   const FooAlias b = FooAlias(GetExampleValue<TypeParam>(0));
   EXPECT_EQ(a, b);
   EXPECT_FALSE(a != b);
   EXPECT_TRUE(a >= b);
   EXPECT_TRUE(a <= b);
   EXPECT_FALSE(a > b);
   EXPECT_FALSE(a < b);
 }

 TYPED_TEST(StrongAliasTest, ComparesCorrectlyToDifferentValue) {
   using FooAlias = StrongAlias<class FooTag, TypeParam>;
   const FooAlias a = FooAlias(GetExampleValue<TypeParam>(0));
   const FooAlias b = FooAlias(GetExampleValue<TypeParam>(1));
   EXPECT_NE(a, b);
   EXPECT_FALSE(a == b);
   EXPECT_TRUE(b >= a);
   EXPECT_TRUE(a <= b);
   EXPECT_TRUE(b > a);
   EXPECT_TRUE(a < b);
 }

 TEST(StrongAliasTest, CanBeDerivedFrom) {
   // Aliases can be enriched by custom operations or validations if needed.
   // Ideally, one could go from a 'using' declaration to a derived class to add
   // those methods without the need to change any other code.
   class CountryCode : public StrongAlias<CountryCode, std::string> {
    public:
     explicit CountryCode(const std::string& value)
         : StrongAlias<CountryCode, std::string>::StrongAlias(value) {
       if (value_.length() != 2) {
         // Country code invalid!
         value_.clear();  // is_null() will return true.
       }
     }

     bool is_null() const { return value_.empty(); }
   };

   CountryCode valid("US");
   EXPECT_FALSE(valid.is_null());

   CountryCode invalid("United States");
   EXPECT_TRUE(invalid.is_null());
 }

 TEST(StrongAliasTest, CanWrapComplexStructures) {
   // A pair of strings implements odering and can, in principle, be used as
   // a base of StrongAlias.
   using PairOfStrings = std::pair<std::string, std::string>;
   using ComplexAlias = StrongAlias<class FooTag, PairOfStrings>;

   ComplexAlias a1{std::make_pair("aaa", "bbb")};
   ComplexAlias a2{std::make_pair("ccc", "ddd")};
   EXPECT_TRUE(a1 < a2);

   EXPECT_TRUE(a1.value() == PairOfStrings("aaa", "bbb"));

   // Note a caveat, an std::pair doesn't have an overload of operator<<, and it
   // cannot be easily added since ADL rules would require it to be in the std
   // namespace. So we can't print ComplexAlias.
 }

 TYPED_TEST(StrongAliasTest, CanBeKeysInFlatMap) {
   using FooAlias = StrongAlias<class FooTag, TypeParam>;
   webrtc::flat_map<FooAlias, std::string> map;

   FooAlias k1(GetExampleValue<TypeParam>(0));
   FooAlias k2(GetExampleValue<TypeParam>(1));

   map[k1] = "value1";
   map[k2] = "value2";

   EXPECT_EQ(map[k1], "value1");
   EXPECT_EQ(map[k2], "value2");
 }

 TYPED_TEST(StrongAliasTest, CanBeKeysInStdMap) {
   using FooAlias = StrongAlias<class FooTag, TypeParam>;
   std::map<FooAlias, std::string> map;

   FooAlias k1(GetExampleValue<TypeParam>(0));
   FooAlias k2(GetExampleValue<TypeParam>(1));

   map[k1] = "value1";
   map[k2] = "value2";

   EXPECT_EQ(map[k1], "value1");
   EXPECT_EQ(map[k2], "value2");
 }

 TYPED_TEST(StrongAliasTest, CanDifferentiateOverloads) {
   using FooAlias = StrongAlias<class FooTag, TypeParam>;
   using BarAlias = StrongAlias<class BarTag, TypeParam>;
   class Scope {
    public:
     static std::string Overload(FooAlias) { return "FooAlias"; }
     static std::string Overload(BarAlias) { return "BarAlias"; }
   };
   EXPECT_EQ("FooAlias", Scope::Overload(FooAlias()));
   EXPECT_EQ("BarAlias", Scope::Overload(BarAlias()));
 }

 TEST(StrongAliasTest, EnsureConstexpr) {
   using FooAlias = StrongAlias<class FooTag, int>;

   // Check constructors.
   static constexpr FooAlias kZero{};
   static constexpr FooAlias kOne(1);

   // Check operator*.
   static_assert(*kZero == 0, "");
   static_assert(*kOne == 1, "");

   // Check value().
   static_assert(kZero.value() == 0, "");
   static_assert(kOne.value() == 1, "");

   // Check explicit conversions to underlying type.
   static_assert(static_cast<int>(kZero) == 0, "");
   static_assert(static_cast<int>(kOne) == 1, "");

   // Check comparison operations.
   static_assert(kZero == kZero, "");
   static_assert(kZero != kOne, "");
   static_assert(kZero < kOne, "");
   static_assert(kZero <= kOne, "");
   static_assert(kOne > kZero, "");
   static_assert(kOne >= kZero, "");
 }

 TEST(StrongAliasTest, BooleansAreEvaluatedAsBooleans) {
   using BoolAlias = StrongAlias<class BoolTag, bool>;

   BoolAlias happy(true);
   BoolAlias sad(false);

   EXPECT_TRUE(happy);
   EXPECT_FALSE(sad);
   EXPECT_TRUE(*happy);
   EXPECT_FALSE(*sad);
 }
 }  // namespace webrtc
	/*
	* Copyright 2019 The Chromium Authors. All rights reserved.
	* Copyright (c) 2021 The WebRTC project authors. All Rights Reserved.
	*
	* Use of this source code is governed by a BSD-style license
	* that can be found in the LICENSE file in the root of the source
	* tree. An additional intellectual property rights grant can be found
	* in the file PATENTS. All contributing project authors may
	* be found in the AUTHORS file in the root of the source tree.
	*/
	#include "rtc_base/strong_alias.h"

	#include <cstdint>
	#include <map>
	#include <memory>
	#include <string>
	#include <type_traits>
	#include <utility>

	#include "rtc_base/containers/flat_map.h"
	#include "rtc_base/gunit.h"
	#include "test/gmock.h"

	// This is a copy of
	// https://source.chromium.org/chromium/chromium/src/+/main:base/types/strong_alias_unittest.cc
	// but adapted to use WebRTC's includes, remove unit tests that test the ostream
	// operator (it's removed in this port) and other adaptations to pass lint.

	namespace webrtc {
	namespace {

	// For test correctnenss, it's important that these getters return lexically
	// incrementing values as `index` grows.
	template <typename T>
	T GetExampleValue(int index);

	template <>
	int GetExampleValue<int>(int index) {
	return 5 + index;
	}
	template <>
	uint64_t GetExampleValue<uint64_t>(int index) {
	return 500U + index;
	}

	template <>
	std::string GetExampleValue<std::string>(int index) {
	return std::string('a', index);
	}

	} // namespace

	template <typename T>
	class StrongAliasTest : public ::testing::Test {};

	using TestedTypes = ::testing::Types<int, uint64_t, std::string>;
	TYPED_TEST_SUITE(StrongAliasTest, TestedTypes);

	TYPED_TEST(StrongAliasTest, ValueAccessesUnderlyingValue) {
	using FooAlias = StrongAlias<class FooTag, TypeParam>;

	// Const value getter.
	const FooAlias const_alias(GetExampleValue<TypeParam>(1));
	EXPECT_EQ(GetExampleValue<TypeParam>(1), const_alias.value());
	static_assert(std::is_const<typename std::remove_reference<decltype(
	const_alias.value())>::type>::value,
	"Reference returned by const value getter should be const.");
	}

	TYPED_TEST(StrongAliasTest, ExplicitConversionToUnderlyingValue) {
	using FooAlias = StrongAlias<class FooTag, TypeParam>;

	const FooAlias const_alias(GetExampleValue<TypeParam>(1));
	EXPECT_EQ(GetExampleValue<TypeParam>(1), static_cast<TypeParam>(const_alias));
	}

	TYPED_TEST(StrongAliasTest, CanBeCopyConstructed) {
	using FooAlias = StrongAlias<class FooTag, TypeParam>;
	FooAlias alias(GetExampleValue<TypeParam>(0));
	FooAlias copy_constructed = alias;
	EXPECT_EQ(copy_constructed, alias);

	FooAlias copy_assigned;
	copy_assigned = alias;
	EXPECT_EQ(copy_assigned, alias);
	}

	TYPED_TEST(StrongAliasTest, CanBeMoveConstructed) {
	using FooAlias = StrongAlias<class FooTag, TypeParam>;
	FooAlias alias(GetExampleValue<TypeParam>(0));
	FooAlias move_constructed = std::move(alias);
	EXPECT_EQ(move_constructed, FooAlias(GetExampleValue<TypeParam>(0)));

	FooAlias alias2(GetExampleValue<TypeParam>(2));
	FooAlias move_assigned;
	move_assigned = std::move(alias2);
	EXPECT_EQ(move_assigned, FooAlias(GetExampleValue<TypeParam>(2)));

	// Check that FooAlias is nothrow move constructible. This matters for
	// performance when used in std::vectors.
	static_assert(std::is_nothrow_move_constructible<FooAlias>::value,
	"Error: Alias is not nothow move constructible");
	}

	TYPED_TEST(StrongAliasTest, CanBeConstructedFromMoveOnlyType) {
	// Note, using a move-only unique_ptr to T:
	using FooAlias = StrongAlias<class FooTag, std::unique_ptr<TypeParam>>;

	FooAlias a(std::make_unique<TypeParam>(GetExampleValue<TypeParam>(0)));
	EXPECT_EQ(*a.value(), GetExampleValue<TypeParam>(0));

	auto bare_value = std::make_unique<TypeParam>(GetExampleValue<TypeParam>(1));
	FooAlias b(std::move(bare_value));
	EXPECT_EQ(*b.value(), GetExampleValue<TypeParam>(1));
	}

	TYPED_TEST(StrongAliasTest, MutableOperatorArrow) {
	// Note, using a move-only unique_ptr to T:
	using Ptr = std::unique_ptr<TypeParam>;
	using FooAlias = StrongAlias<class FooTag, Ptr>;

	FooAlias a(std::make_unique<TypeParam>());
	EXPECT_TRUE(a.value());

	// Check that `a` can be modified through the use of operator->.
	a->reset();

	EXPECT_FALSE(a.value());
	}

	TYPED_TEST(StrongAliasTest, MutableOperatorStar) {
	// Note, using a move-only unique_ptr to T:
	using Ptr = std::unique_ptr<TypeParam>;
	using FooAlias = StrongAlias<class FooTag, Ptr>;

	FooAlias a(std::make_unique<TypeParam>());
	FooAlias b(std::make_unique<TypeParam>());
	EXPECT_TRUE(*a);
	EXPECT_TRUE(*b);

	// Check that both the mutable l-value and r-value overloads work and we can
	// move out of the aliases.
	{ Ptr ignore(*std::move(a)); }
	{ Ptr ignore(std::move(*b)); }

	EXPECT_FALSE(a.value());
	EXPECT_FALSE(b.value());
	}

	TYPED_TEST(StrongAliasTest, MutableValue) {
	// Note, using a move-only unique_ptr to T:
	using Ptr = std::unique_ptr<TypeParam>;
	using FooAlias = StrongAlias<class FooTag, Ptr>;

	FooAlias a(std::make_unique<TypeParam>());
	FooAlias b(std::make_unique<TypeParam>());
	EXPECT_TRUE(a.value());
	EXPECT_TRUE(b.value());

	// Check that both the mutable l-value and r-value overloads work and we can
	// move out of the aliases.
	{ Ptr ignore(std::move(a).value()); }
	{ Ptr ignore(std::move(b.value())); }

	EXPECT_FALSE(a.value());
	EXPECT_FALSE(b.value());
	}

	TYPED_TEST(StrongAliasTest, SizeSameAsUnderlyingType) {
	using FooAlias = StrongAlias<class FooTag, TypeParam>;
	static_assert(sizeof(FooAlias) == sizeof(TypeParam),
	"StrongAlias should be as large as the underlying type.");
	}

	TYPED_TEST(StrongAliasTest, IsDefaultConstructible) {
	using FooAlias = StrongAlias<class FooTag, TypeParam>;
	static_assert(std::is_default_constructible<FooAlias>::value,
	"Should be possible to default-construct a StrongAlias.");
	static_assert(
	std::is_trivially_default_constructible<FooAlias>::value ==
	std::is_trivially_default_constructible<TypeParam>::value,
	"Should be possible to trivially default-construct a StrongAlias iff the "
	"underlying type is trivially default constructible.");
	}

	TEST(StrongAliasTest, TrivialTypeAliasIsStandardLayout) {
	using FooAlias = StrongAlias<class FooTag, int>;
	static_assert(std::is_standard_layout<FooAlias>::value,
	"int-based alias should have standard layout. ");
	static_assert(std::is_trivially_copyable<FooAlias>::value,
	"int-based alias should be trivially copyable. ");
	}

	TYPED_TEST(StrongAliasTest, CannotBeCreatedFromDifferentAlias) {
	using FooAlias = StrongAlias<class FooTag, TypeParam>;
	using BarAlias = StrongAlias<class BarTag, TypeParam>;
	static_assert(!std::is_constructible<FooAlias, BarAlias>::value,
	"Should be impossible to construct FooAlias from a BarAlias.");
	static_assert(!std::is_convertible<BarAlias, FooAlias>::value,
	"Should be impossible to convert a BarAlias into FooAlias.");
	}

	TYPED_TEST(StrongAliasTest, CannotBeImplicitlyConverterToUnderlyingValue) {
	using FooAlias = StrongAlias<class FooTag, TypeParam>;
	static_assert(!std::is_convertible<FooAlias, TypeParam>::value,
	"Should be impossible to implicitly convert a StrongAlias into "
	"an underlying type.");
	}

	TYPED_TEST(StrongAliasTest, ComparesEqualToSameValue) {
	using FooAlias = StrongAlias<class FooTag, TypeParam>;
	// Comparison to self:
	const FooAlias a = FooAlias(GetExampleValue<TypeParam>(0));
	EXPECT_EQ(a, a);
	EXPECT_FALSE(a != a);
	EXPECT_TRUE(a >= a);
	EXPECT_TRUE(a <= a);
	EXPECT_FALSE(a > a);
	EXPECT_FALSE(a < a);
	// Comparison to other equal object:
	const FooAlias b = FooAlias(GetExampleValue<TypeParam>(0));
	EXPECT_EQ(a, b);
	EXPECT_FALSE(a != b);
	EXPECT_TRUE(a >= b);
	EXPECT_TRUE(a <= b);
	EXPECT_FALSE(a > b);
	EXPECT_FALSE(a < b);
	}

	TYPED_TEST(StrongAliasTest, ComparesCorrectlyToDifferentValue) {
	using FooAlias = StrongAlias<class FooTag, TypeParam>;
	const FooAlias a = FooAlias(GetExampleValue<TypeParam>(0));
	const FooAlias b = FooAlias(GetExampleValue<TypeParam>(1));
	EXPECT_NE(a, b);
	EXPECT_FALSE(a == b);
	EXPECT_TRUE(b >= a);
	EXPECT_TRUE(a <= b);
	EXPECT_TRUE(b > a);
	EXPECT_TRUE(a < b);
	}

	TEST(StrongAliasTest, CanBeDerivedFrom) {
	// Aliases can be enriched by custom operations or validations if needed.
	// Ideally, one could go from a 'using' declaration to a derived class to add
	// those methods without the need to change any other code.
	class CountryCode : public StrongAlias<CountryCode, std::string> {
	public:
	explicit CountryCode(const std::string& value)
	: StrongAlias<CountryCode, std::string>::StrongAlias(value) {
	if (value_.length() != 2) {
	// Country code invalid!
	value_.clear(); // is_null() will return true.
	}
	}

	bool is_null() const { return value_.empty(); }
	};

	CountryCode valid("US");
	EXPECT_FALSE(valid.is_null());

	CountryCode invalid("United States");
	EXPECT_TRUE(invalid.is_null());
	}

	TEST(StrongAliasTest, CanWrapComplexStructures) {
	// A pair of strings implements odering and can, in principle, be used as
	// a base of StrongAlias.
	using PairOfStrings = std::pair<std::string, std::string>;
	using ComplexAlias = StrongAlias<class FooTag, PairOfStrings>;

	ComplexAlias a1{std::make_pair("aaa", "bbb")};
	ComplexAlias a2{std::make_pair("ccc", "ddd")};
	EXPECT_TRUE(a1 < a2);

	EXPECT_TRUE(a1.value() == PairOfStrings("aaa", "bbb"));

	// Note a caveat, an std::pair doesn't have an overload of operator<<, and it
	// cannot be easily added since ADL rules would require it to be in the std
	// namespace. So we can't print ComplexAlias.
	}

	TYPED_TEST(StrongAliasTest, CanBeKeysInFlatMap) {
	using FooAlias = StrongAlias<class FooTag, TypeParam>;
	webrtc::flat_map<FooAlias, std::string> map;

	FooAlias k1(GetExampleValue<TypeParam>(0));
	FooAlias k2(GetExampleValue<TypeParam>(1));

	map[k1] = "value1";
	map[k2] = "value2";

	EXPECT_EQ(map[k1], "value1");
	EXPECT_EQ(map[k2], "value2");
	}

	TYPED_TEST(StrongAliasTest, CanBeKeysInStdMap) {
	using FooAlias = StrongAlias<class FooTag, TypeParam>;
	std::map<FooAlias, std::string> map;

	FooAlias k1(GetExampleValue<TypeParam>(0));
	FooAlias k2(GetExampleValue<TypeParam>(1));

	map[k1] = "value1";
	map[k2] = "value2";

	EXPECT_EQ(map[k1], "value1");
	EXPECT_EQ(map[k2], "value2");
	}

	TYPED_TEST(StrongAliasTest, CanDifferentiateOverloads) {
	using FooAlias = StrongAlias<class FooTag, TypeParam>;
	using BarAlias = StrongAlias<class BarTag, TypeParam>;
	class Scope {
	public:
	static std::string Overload(FooAlias) { return "FooAlias"; }
	static std::string Overload(BarAlias) { return "BarAlias"; }
	};
	EXPECT_EQ("FooAlias", Scope::Overload(FooAlias()));
	EXPECT_EQ("BarAlias", Scope::Overload(BarAlias()));
	}

	TEST(StrongAliasTest, EnsureConstexpr) {
	using FooAlias = StrongAlias<class FooTag, int>;

	// Check constructors.
	static constexpr FooAlias kZero{};
	static constexpr FooAlias kOne(1);

	// Check operator*.
	static_assert(*kZero == 0, "");
	static_assert(*kOne == 1, "");

	// Check value().
	static_assert(kZero.value() == 0, "");
	static_assert(kOne.value() == 1, "");

	// Check explicit conversions to underlying type.
	static_assert(static_cast<int>(kZero) == 0, "");
	static_assert(static_cast<int>(kOne) == 1, "");

	// Check comparison operations.
	static_assert(kZero == kZero, "");
	static_assert(kZero != kOne, "");
	static_assert(kZero < kOne, "");
	static_assert(kZero <= kOne, "");
	static_assert(kOne > kZero, "");
	static_assert(kOne >= kZero, "");
	}

	TEST(StrongAliasTest, BooleansAreEvaluatedAsBooleans) {
	using BoolAlias = StrongAlias<class BoolTag, bool>;

	BoolAlias happy(true);
	BoolAlias sad(false);

	EXPECT_TRUE(happy);
	EXPECT_FALSE(sad);
	EXPECT_TRUE(*happy);
	EXPECT_FALSE(*sad);
	}
	} // namespace webrtc