What are true and false operators in C#?

Question

What is the purpose and effect of the true and false operators in C#? The official documentation on these is hopelessly non-explanatory.

Answer 1

See the referenced example in the article

C# Language Specification -- Database boolean type

Essentially these operators allow an instance of a type to be used in boolean conditional logic such as && and ||.

Answer 2

They allow you to overload them using the operator overloading syntax so that a type you define can be interpreted as a boolean.

Answer 3

The allow you to use a custom type as a part of logic operations; For example, as part of an if or while statement.

Answer 4

You would overload the true or false operators if you were defining a specialized boolean value. This is not typically needed, however, which is why they don't seem useful. For example, in a fuzzy-logic boolean class, you might have something like this:

// Represents a boolean that can store truth values in a range from [0, 1], with
//   a value of one indicating complete metaphysical certitude and a value of
//   zero indicating complete impossibility.
public class FuzzyBoolean {
// ...
   public static bool operator true(FuzzyBoolean fb) {
      return fb.TruthValue > 0;
   }

   public static bool operator false(FuzzyBoolean fb) {
      return fb.TruthValue == 0;
   }
// ...
}

Note that if you overload true, you must also overload false (and vice versa).

Of course, there are also the true and false literals, the two literal values you can assign to a boolean instance. Don't confuse these with the operators mentioned above. A more substantial example of how you'd use this, involving booleans in a database, is given in the MSDN docs here.

Answer 5

The true and false operators can be overloaded, to allow a class to represent its own state as true or false, for example:

public class MyClass
{
    //...
    public static bool operator true(MyClass op)
    {
        // Evaluation code...
    }

    public static bool operator false(MyClass op)
    {
        // Evaluation code...
    }
}

And you will be able to use the operator in boolean expressions:

MyClass test = new MyClass(4, 3);
if (test)
    Console.WriteLine("Something true");
else
    Console.WriteLine("Something false");

string text = test ? "Returned true" : "Returned false";