518.4 Struct examples

14

// The Null member represents an unknown DBInt value.

15

public static readonly DBInt Null = new DBInt();

16

// When the defined field is true, this DBInt represents a

17

// known value which is stored in the value field. When

18

// the defined field is false, this DBInt represents an

19

// unknown value, and the value field is 0.

20

int value;

21

bool defined;

22

// Private instance constructor. Creates a DBInt with a known value.

23

DBInt(int value) {

24

this.value = value;

25

this.defined = true;

26

}

27

// The IsNull property is true if this DBInt represents an unknown

28

// value.

29

public bool IsNull { get { return !defined; } }

30

// The Value property is the known value of this DBInt, or 0 if this

31

// DBInt represents an unknown value.

32

public int Value { get { return value; } }

33

// Implicit conversion from int to DBInt.

34

public static implicit operator DBInt(int x) {

35

return new DBInt(x);

36

}

37

// Explicit conversion from DBInt to int. Throws an exception if the

38

// given DBInt represents an unknown value.

39

public static explicit operator int(DBInt x) {

40

if (!x.defined) throw new InvalidOperationException();

41

return x.value;

42

}

43

public static DBInt operator +(DBInt x) {

44

return x;

45

}

46

public static DBInt operator -(DBInt x) {

47

return x.defined? -x.value: Null;

48

}

49

public static DBInt operator +(DBInt x, DBInt y) {

50

return x.defined && y.defined? x.value + y.value: Null;

51

}

Chapter 18 Structs

1

public static DBInt operator -(DBInt x, DBInt y) {

2

return x.defined && y.defined? x.value - y.value: Null;

3

}

4

public static DBInt operator *(DBInt x, DBInt y) {

5

return x.defined && y.defined? x.value * y.value: Null;

6

}

7

public static DBInt operator /(DBInt x, DBInt y) {

8

return x.defined && y.defined? x.value / y.value: Null;

9

}

10

public static DBInt operator %(DBInt x, DBInt y) {

11

return x.defined && y.defined? x.value % y.value: Null;

12

}

13

public static DBBool operator ==(DBInt x, DBInt y) {

14

return x.defined && y.defined? x.value == y.value: DBBool.Null;

15

}

16

public static DBBool operator !=(DBInt x, DBInt y) {

17

return x.defined && y.defined? x.value != y.value: DBBool.Null;

18

}

19

public static DBBool operator >(DBInt x, DBInt y) {

20

return x.defined && y.defined? x.value > y.value: DBBool.Null;

21

}

22

public static DBBool operator <(DBInt x, DBInt y) {

23

return x.defined && y.defined? x.value < y.value: DBBool.Null;

24

}

25

public static DBBool operator >=(DBInt x, DBInt y) {

26

return x.defined && y.defined? x.value >= y.value: DBBool.Null;

27

}

28

public static DBBool operator <=(DBInt x, DBInt y) {

29

return x.defined && y.defined? x.value <= y.value: DBBool.Null;

39

// The three possible DBBool values.

40

public static readonly DBBool Null = new DBBool(0);

41

public static readonly DBBool False = new DBBool(-1);

42

public static readonly DBBool True = new DBBool(1);

43

// Private field that stores –1, 0, 1 for False, Null, True.

44

sbyte value;

45

// Private instance constructor. The value parameter must be

46

// –1, 0, or 1.

47

DBBool(int value) {

48

this.value = (sbyte)value;

49

}

50

// Properties to examine the value of a DBBool. Return true if this

51

// DBBool has the given value, false otherwise.

52

public bool IsNull { get { return value == 0; } }

53

public bool IsFalse { get { return value < 0; } }

54

public bool IsTrue { get { return value > 0; } }

C# LANGUAGE SPECIFICATION

1

// Implicit conversion from bool to DBBool. Maps true to

2

// DBBool.True and false to DBBool.False.

3

public static implicit operator DBBool(bool x) {

4

return x? True: False;

5

}

6

// Explicit conversion from DBBool to bool. Throws an exception

7

// if the given DBBool is Null, otherwise returns true or false.

8

public static explicit operator bool(DBBool x) {

9

if (x.value == 0) throw new InvalidOperationException();

10

return x.value > 0;

11

}

12

// Equality operator. Returns Null if either operand is Null,

13

// otherwise returns True or False.

14

public static DBBool operator ==(DBBool x, DBBool y) {

15

if (x.value == 0 || y.value == 0) return Null;

16

return x.value == y.value? True: False;

17

}

18

// Inequality operator. Returns Null if either operand is Null,

19

// otherwise returns True or False.

20

public static DBBool operator !=(DBBool x, DBBool y) {

21

if (x.value == 0 || y.value == 0) return Null;

22

return x.value != y.value? True: False;

23

}

24

// Logical negation operator. Returns True if the operand is False,

25

// Null if the operand is Null, or False if the operand is True.

26

public static DBBool operator !(DBBool x) {

27

return new DBBool(-x.value);

28

}

29

// Logical AND operator. Returns False if either operand is False,

30

// otherwise Null if either operand is Null, otherwise True.

31

public static DBBool operator &(DBBool x, DBBool y) {

32

return new DBBool(x.value < y.value? x.value: y.value);

33

}

34

// Logical OR operator. Returns True if either operand is True,

35

// otherwise Null if either operand is Null, otherwise False.

36

public static DBBool operator |(DBBool x, DBBool y) {

37

return new DBBool(x.value > y.value? x.value: y.value);

38

}

39

// Definitely true operator. Returns true if the operand is True,

40

// false otherwise.

41

public static bool operator true(DBBool x) {

42

return x.value > 0;

43

}

44

// Definitely false operator. Returns true if the operand is False,

45

// false otherwise.

46

public static bool operator false(DBBool x) {

47

return x.value < 0;