C# Error
CS0559 – The parameter type for ++ or — operator must be the containing type
Reason for the Error & Solution
The parameter type for ++ or — operator must be the containing type
The method declaration for an operator overload must follow certain guidelines. For the ++ and — operators, it is required that the parameter be of the same type as the type in which the operator is being overloaded.
Example 1
The following sample generates CS0559:
// CS0559.cs
// compile with: /target:library
public class iii
{
public static implicit operator int(iii x)
{
return 0;
}
public static implicit operator iii(int x)
{
return null;
}
public static int operator ++(int aa) // CS0559
// try the following line instead
// public static iii operator ++(iii aa)
{
return (iii)0;
}
}
Example 2
The following sample generates CS0559.
// CS0559_b.cs
// compile with: /target:library
public struct S
{
public static S operator ++(S? s) { return new S(); } // CS0559
public static S operator --(S? s) { return new S(); } // CS0559
}
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(); }
}
