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Compiler Error CS0218

The type ('type') must contain declarations of operator true and operator false

If you define an operator for a user-defined type, and then try to use the operator as a short-circuit operator, the user-defined operator must have operator true and operator false defined. For more information on short-circuit operators, see && Operator and || Operator.

The following sample generates CS0218:

// CS0218.cs
using System;
public class MyClass
{
   // uncomment these operator declarations to resolve this CS0218
   /*
   public static bool operator true (MyClass f)
   {
      return false;
   }

   public static bool operator false (MyClass f)
   {
      return false;
   }
   */

   public static implicit operator int(MyClass x)
   {
      return 0;
   }

   public static MyClass operator & (MyClass f1, MyClass f2)
   {
      return new MyClass();
   }

   public static void Main()
   {
      MyClass f = new MyClass();
      int i = f && f;   // CS0218, requires operators true and false
   }
}
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