Question

There are two weird operators in C#:

• the true operator
• the false operator

If I understand this right these operators can be used in types which I want to use instead of a boolean expression and where I don’t want to provide an implicit conversion to bool.

Let’s say I have a following class:

    public class MyType     {         public readonly int Value;          public MyType(int value)         {             Value = value;         }          public static bool operator true (MyType mt)         {             return  mt.Value > 0;         }          public static bool operator false (MyType mt)         {             return  mt.Value < 0;         }      } 

So I can write the following code:

    MyType mTrue = new MyType(100);     MyType mFalse = new MyType(-100);     MyType mDontKnow = new MyType(0);      if (mTrue)     {          // Do something.     }      while (mFalse)     {         // Do something else.     }      do     {         // Another code comes here.     } while (mDontKnow) 

However for all the examples above only the true operator is executed. So what’s the false operator in C# good for?

Note: More examples can be found here, here and here.

Answer 1

You can use it to override the && and || operators.

The && and || operators can’t be overridden, but if you override |, &, true and false in exactly the right way the compiler will call | and & when you write || and &&.

For example, look at this code (from http://ayende.com/blog/1574/nhibernate-criteria-api-operator-overloading – where I found out about this trick; archived version by @BiggsTRC):

public static AbstractCriterion operator &(AbstractCriterion lhs, AbstractCriterion rhs) {        return new AndExpression(lhs, rhs); }  public static AbstractCriterion operator |(AbstractCriterion lhs, AbstractCriterion rhs) {        return new OrExpression(lhs, rhs); }  public static bool operator false(AbstractCriterion criteria) {        return false; } public static bool operator true(AbstractCriterion criteria) {        return false; } 

This is obviously a side effect and not the way it’s intended to be used, but it is useful.