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:
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 } }