C＃中的真假运算符是什么？

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

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 2

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";

Answer 3

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 4

Prior to C# 2.0, the true and false operators were used to create user-defined nullable value types that were compatible with types such as SqlBool. However, the language now provides built-in support for nullable value types, and whenever possible you should use those instead of overloading the true and false operators. For more information.With nullable Booleans, the expression a != b is not necessarily equal to !(a == b) because one or both of the values might be null. You need to overload both the true and false operators separately to correctly identify the null values in the expression. The following example shows how to overload and use the true and false operators.

Answer 5

它们允许您使用运算符重载语法重载它们，以便您定义的类型可以解释为布尔值。

Answer 6

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