Database boolean type

The DBBool struct below implements a three-valued logical type. The possible values of this type are DBBool.True, DBBool.False, and DBBool.Null, where the Null member indicates an unknown value. Such three-valued logical types are commonly used in databases. using System; public struct DBBool { // The three possible DBBool values. public static readonly DBBool Null = new DBBool(0); public static readonly DBBool False = new DBBool(-1); public static readonly DBBool True = new DBBool(1); // Private field that stores -1, 0, 1 for False, Null, True. sbyte value; // Private instance constructor. The value parameter must be -1, 0, or 1. DBBool(int value) { this.value = (sbyte)value; } // Properties to examine the value of a DBBool. Return true if this // DBBool has the given value, false otherwise. public bool IsNull { get { return value == 0; } } public bool IsFalse { get { return value < 0; } } public bool IsTrue { get { return value > 0; } } // Implicit conversion from bool to DBBool. Maps true to DBBool.True // and false to DBBool.False. public static implicit operator DBBool(bool x) { return x? True: False; } // Explicit conversion from DBBool to bool. Throws an exception if the // given DBBool is Null, otherwise returns true or false. public static explicit operator bool(DBBool x) { if (x.value == 0) throw new InvalidOperationException(); return x.value > 0; } // Equality operator. Returns Null if either operand is Null, // otherwise returns True or False. public static DBBool operator ==(DBBool x, DBBool y) { if (x.value == 0 || y.value == 0) return Null; return x.value == y.value? True: False; } // Inequality operator. Returns Null if either operand is Null, // otherwise returns True or False. public static DBBool operator !=(DBBool x, DBBool y) { if (x.value == 0 || y.value == 0) return Null; return x.value != y.value? True: False; } // Logical negation operator. Returns True if the operand is False, // Null if the operand is Null, or False if the operand is True. public static DBBool operator !(DBBool x) { return new DBBool(-x.value); } // Logical AND operator. Returns False if either operand is False, // otherwise Null if either operand is Null, otherwise True. public static DBBool operator &(DBBool x, DBBool y) { return new DBBool(x.value < y.value? x.value: y.value); } // Logical OR operator. Returns True if either operand is True, // otherwise Null if either operand is Null, otherwise False. public static DBBool operator |(DBBool x, DBBool y) { return new DBBool(x.value > y.value? x.value: y.value); } // Definitely true operator. Returns true if the operand is True, // false otherwise. public static bool operator true(DBBool x) { return x.value > 0; } // Definitely false operator. Returns true if the operand is False, // false otherwise. public static bool operator false(DBBool x) { return x.value < 0; } }
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