Overloading Operators in C# - Overloading true and false
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The true and false operators are used in the extremely rare case of operators defining types with three-state logic to enable these types to work seamlessly with conditional statements and operators—namely, the if, do, while,for, and?:. TheSystem.Data.SqlTypes.SqlBooleanstruct provides this functionality. For example:
class Test
{
static void Main()
{
SqlBoolean a = SqlBoolean.Null;
if (a)
Console.WriteLine("True");
else if (! a)
Console.WriteLine("False");
else
Console.WriteLine("Null");
}
}
OUTPUT:
Null
The following code is a reimplementation of the parts ofSqlBooleannecessary to demonstrate thetrueandfalseoperators:
public struct SqlBoolean
{
public static bool operator true (SqlBoolean x)
{
return x.m_value == True.m_value;
}
public static bool operator false (SqlBoolean x)
{
return x.m_value == False.m_value;
}
public static SqlBoolean operator !(SqlBoolean x)
{
if (x.m_value == Null.m_value) return Null;
if (x.m_value == False.m_value) return True;
return False;
}
public static readonly SqlBoolean Null = new SqlBoolean(0);
public static readonly SqlBoolean False = new SqlBoolean(1);
public static readonly SqlBoolean True = new SqlBoolean(2);
private SqlBoolean (byte value) {m_value = value;}
private byte m_value;
}
Please check back next week for the continuation of this article.
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 This article is excerpted from chapter four of C# 3.0 in a Nutshell, Third Edition, A Desktop Quick Reference, written by Joseph Albahari and Ben Albahari (O'Reilly; ISBN: 0596527578). Check it out today at your favorite bookstore. Buy this book now.
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