Question

Given that in .NET the System.String class is sealed, how do you create a simple domain-specific string class so you can use type checking to ensure that the correct sort of string is used? Do you have a favourite implementation of such a class?

You might, for example, want to create a class to represent an email address to ensure that email is not accidentally sent to someone’s postal address. Although that’s not a great example I’m thinking about the cases where all you need is the type safety but no additional logic or validation.

Answer 1

You can wrap the string class in one of your own and add all the type checking you want.

Think composition, instead of inheritance.