Lvalue, Rvalue, Xvalue, Prvalue, Glvalue

c++11中关于什么是lvalue, 什么是rvalue, 什么是xvalue, 什么是prvalue, 什么是…

一直搞得我晕头转向的, 今天下定决心一定要把它搞定, 写了一个程序来判断lvalue, rvalue, prvalue等

 1 namespace test{

 2 

 3 template <typename T>

 4 struct is_lvalue_reference {

 5   const static bool value = false;

 6 };

 7 

 8 template <typename T>

 9 struct is_lvalue_reference<T&> {

10   const static bool value = true;

11 };

12 

13 template <typename T>

14 struct is_rvalue_reference {

15   const static bool value = false;

16 };

17 

18 template <typename T>

19 struct is_rvalue_reference<T&&> {

20   const static bool value = true;

21 };

22 

23 template <typename T>

24 struct is_xvalue {

25   const static bool value = (!is_lvalue_reference<T>::value) && is_rvalue_reference<T>::value;

26 };

27 

28 template <typename T>

29 struct is_prvalue {

30   const static bool value = !(is_lvalue_reference<T>::value || is_rvalue_reference<T>::value);

31 };

32 

33 template <typename T>

34 struct is_lvalue {

35   const static bool value = !(is_xvalue<T>::value || is_prvalue<T>::value);

36 };

37 

38 template <typename T>

39 struct is_rvalue {

40   const static bool value = (is_xvalue<T>::value || is_prvalue<T>::value);

41 };

42 

43 

44 template <typename T>

45 struct is_glvalue{

46   const static bool value = (is_xvalue<T>::value || is_lvalue<T>::value);

47 };

48 

49 }

测试验证:

 1 struct Foo {};

 2 Foo funRetFoo();

 3 Foo& funRetFooLRef();

 4 Foo&& funRetFooRRef();

 5 

 6 

 7 TEST(TypeTraits, isRvalue){

 8 

 9 

10     //base type

11     EXPECT_FALSE(::test::is_lvalue_reference<int>::value);

12     EXPECT_FALSE(::test::is_rvalue_reference<int>::value);

13     EXPECT_FALSE(::test::is_lvalue<int>::value);

14     EXPECT_FALSE(::test::is_xvalue<int>::value);

15     EXPECT_TRUE(::test::is_prvalue<int>::value);

16     EXPECT_FALSE(::test::is_glvalue<int>::value);

17     EXPECT_TRUE(::test::is_rvalue<int>::value);

18 

19     // return obj

20     EXPECT_FALSE(::test::is_lvalue_reference<decltype(funRetFoo())>::value);

21     EXPECT_FALSE(::test::is_rvalue_reference<decltype(funRetFoo())>::value);

22     EXPECT_FALSE(::test::is_lvalue<decltype(funRetFoo())>::value);

23     EXPECT_FALSE(::test::is_xvalue<decltype(funRetFoo())>::value);

24     EXPECT_TRUE(::test::is_prvalue<decltype(funRetFoo())>::value);

25     EXPECT_FALSE(::test::is_glvalue<decltype(funRetFoo())>::value);

26     EXPECT_TRUE(::test::is_rvalue<decltype(funRetFoo())>::value);

27 

28 

29     // return ref obj

30     EXPECT_TRUE(::test::is_lvalue_reference<decltype(funRetFooLRef())>::value);

31     EXPECT_FALSE(::test::is_rvalue_reference<decltype(funRetFooLRef())>::value);

32     EXPECT_TRUE(::test::is_lvalue<decltype(funRetFooLRef())>::value);

33     EXPECT_FALSE(::test::is_xvalue<decltype(funRetFooLRef())>::value);

34     EXPECT_FALSE(::test::is_prvalue<decltype(funRetFooLRef())>::value);

35     EXPECT_TRUE(::test::is_glvalue<decltype(funRetFooLRef())>::value);

36     EXPECT_FALSE(::test::is_rvalue<decltype(funRetFooLRef())>::value);

37 

38     // return rref obj

39     EXPECT_FALSE(::test::is_lvalue_reference<decltype(funRetFooRRef())>::value);

40     EXPECT_TRUE(::test::is_rvalue_reference<decltype(funRetFooRRef())>::value);

41     EXPECT_FALSE(::test::is_lvalue<decltype(funRetFooRRef())>::value);

42     EXPECT_TRUE(::test::is_xvalue<decltype(funRetFooRRef())>::value);

43     EXPECT_FALSE(::test::is_prvalue<decltype(funRetFooRRef())>::value);

44     EXPECT_TRUE(::test::is_glvalue<decltype(funRetFooRRef())>::value);

45     EXPECT_TRUE(::test::is_rvalue<decltype(funRetFooRRef())>::value);

46 

47 

48     int lvalue;

49     // 模拟=号左边

50     EXPECT_TRUE(::test::is_lvalue_reference<decltype(*&lvalue)>::value);

51     EXPECT_FALSE(::test::is_rvalue_reference<decltype(*&lvalue)>::value);

52     EXPECT_TRUE(::test::is_lvalue<decltype(*&lvalue)>::value);

53     EXPECT_FALSE(::test::is_xvalue<decltype(*&lvalue)>::value);

54     EXPECT_FALSE(::test::is_prvalue<decltype(*&lvalue)>::value);

55     EXPECT_TRUE(::test::is_glvalue<decltype(*&lvalue)>::value);

56     EXPECT_FALSE(::test::is_rvalue<decltype(*&lvalue)>::value);

57 

58 

59     //operator++()

60     EXPECT_FALSE(::test::is_lvalue_reference<decltype(lvalue++)>::value);

61     EXPECT_FALSE(::test::is_rvalue_reference<decltype(lvalue++)>::value);

62     EXPECT_FALSE(::test::is_lvalue<decltype(lvalue++)>::value);

63     EXPECT_FALSE(::test::is_xvalue<decltype(lvalue++)>::value);

64     EXPECT_TRUE(::test::is_prvalue<decltype(lvalue++)>::value);

65     EXPECT_FALSE(::test::is_glvalue<decltype(lvalue++)>::value);

66     EXPECT_TRUE(::test::is_rvalue<decltype(lvalue++)>::value);

67 

68     //operator++(int)

69     EXPECT_TRUE(::test::is_lvalue_reference<decltype(++lvalue)>::value);

70     EXPECT_FALSE(::test::is_rvalue_reference<decltype(++lvalue)>::value);

71     EXPECT_TRUE(::test::is_lvalue<decltype(++lvalue)>::value);

72     EXPECT_FALSE(::test::is_xvalue<decltype(++lvalue)>::value);

73     EXPECT_FALSE(::test::is_prvalue<decltype(++lvalue)>::value);

74     EXPECT_TRUE(::test::is_glvalue<decltype(++lvalue)>::value);

75     EXPECT_FALSE(::test::is_rvalue<decltype(++lvalue)>::value);

76 

77 }