Use of project-specific values with enum defined in class library

Question

We have an enum in a class library:

Public Enum FieldType
 Phone
 Span
 Gender
 DrawPath
 ....
End Enum

which we use with an attribute applied to properties, for multiple scenarios: HTML/CSV rendering, onscreen display formatting among them.

Multiple projects use this class library, and we want to use project-specific values with this enum. The class library could have extension points (e.g. Public Shared FieldTypeAsHtml As Func(Of FieldType,String)) which specific projects could override.

Each project could have its own additional enums or constants, and the conversions would be automatic (at least in VB.NET which is what we are using; C# would require explicit conversions).

Aside from the obvious -- the intention of this enum is to be "open" and not limited to a specified set of values, therefore no compile-time safety on a given value -- is this a valid design? Are there any downsides? Since there are no partial enums in .NET, what other alternatives might be better, and why?

• Doc Brown: This question was already discussed on Stackoverflow (more than once), see stackoverflow.com/questions/757684/enum-inheritance
• user20416: @DocBrown The primary thrust of my question is on the advisability/inadvisability of doing this, which is not covered by the SO question.
• Doc Brown: Is it advisable to write programs in a typesafe manner? Short answer: it depends. Sometimes yes, sometimes no, and the reasoning about this will be pretty much the same as to your question.

Answer 1

You could use the "Smart Enum" pattern. It is intended to be extended and typesafe. Although I have C# posts about it, but I think it would be helpful anyway. See:

• Introducing the Type-Safe Enum Pattern
• Jon Skeet's warning of misusings
• Smart Enums
• Generic Approach

• Alexander Y.: Also: Smart Enums and some generic approach.