Compiler Error CS0448

The return type for ++ or -- operator must be the containing type or derived from the containing type

When you override the ++ or -- operators, they must return the same type as the containing type, or return a type that is derived from the containing type.

Example

The following sample generates CS0448.

// CS0448.cs  
class C5  
{  
   public static int operator ++(C5 c) { return null; }   // CS0448  
   public static C5 operator --(C5 c) { return null; }   // OK  
   public static void Main() {}  
}  

Example

The following sample generates CS0448.

// CS0448_b.cs  
public struct S  
{  
   public static S? operator ++(S s) { return new S(); }   // CS0448  
   public static S? operator --(S s) { return new S(); }   // CS0448  
}  
  
public struct T  
{  
// OK  
   public static T operator --(T t) { return new T(); }  
   public static T operator ++(T t) { return new T(); }  
  
   public static T? operator --(T? t) { return new T(); }  
   public static T? operator ++(T? t) { return new T(); }  
  
   public static void Main() {}  
}