How to associate constants with an interface in C#?

Question

Some languages let you associate a constant with an interface:

• A Java example
• A PhP example

The W3C abstract interfaces do the same, for example:

// Introduced in DOM Level 2:
interface CSSValue {

  // UnitTypes
  const unsigned short      CSS_INHERIT                    = 0;
  const unsigned short      CSS_PRIMITIVE_VALUE            = 1;
  const unsigned short      CSS_VALUE_LIST                 = 2;
  const unsigned short      CSS_CUSTOM                     = 3;

  attribute DOMString       cssText;
  attribute unsigned short  cssValueType;
};

I want to define this interface such that it can be called from C#.

Apparently C# cannot define a constant associated with an interface.

• What is the usual way to translate such an interface to C#?
• Are there any 'canonical' C# bindings for the DOM interfaces?
• Although C# cannot, is there another .NET language which can define constants associated with an interface?

Answer 1

To answer your third question:

Although C# cannot, is there another .NET language which can define constants associated with an interface?

C++/CLI allows you to define literal values in an interface, which are equivalent to static const values in C#.

public interface class ICSSValue
{
public:
    literal short CSS_INHERIT = 0;
    literal short CSS_PRIMITIVE_VALUE = 1;
    literal short CSS_VALUE_LIST = 2;
    literal short CSS_CSS_CUSTOM = 3;

    property DOMString^ cssText;
    property ushort cssValueType;
}

You could then access the values via C#:

public static void Main()
{
    short primitiveValue = ICSSValue.CSS_PRIMITIVE_VALUE;

    Debug.Assert(primitiveValue == 1);
}

See this page on MSDN for more details.

Disclaimer: The design decision to disallow constant values in interfaces was a good one. An interface which exposes implementation details is most likely a leaky abstraction. In this example CSS Value Type is probably better off being an enumeration.