Have a class behave like a string

Question

Is it possible to have a class that behaves like a string but allows me to have some additional properties?

Specifically, I want to be able to do something like

Dim A As MyClass ''Or New MyClass("InitialValue")
A = "Something"
If A = "SomethingElse" Then

End If

From what I can see, I need to implement a type that can be assigned in such a way that it's passed the string in a constructor:

eg A = Something should be interpreted as A = New MyClass("Something"). In addition, I then need to override the comparison operator so that If A = "SomethingElse" Then can be handled by my code which checks the underlying String value

Since String is sealed/not inheritable and String seems to have some special handling in .Net I'm a little stumped as to how to approach this.

To explain why it's required, I've got an entity class (Not EF) which is serialized to generate queries against a search index. The queries are created by specifying a lambda against my entity.

I now need to modify certain properties on the entity so that instead of serializing to a simple string (for passing to the search index), they're complex objects. I don't have control over the serialization itself (currently being handled inside Newtonsoft Json.Net) so I was hoping this would be a (quicker) alternative which would allow me to use the existing lambdas, etc...

Answer 1

You can do this for the assignment using a custom implicit conversion from System.String, as XNamespace does, for example¹. Whether that would also work for the comparison, I'm not sure.

I'm generally very nervous of implicit conversions, and would urge caution around this. Having a constructor or static factory method, or possibly an extension method to convert from string to the relevant type, would make this clearer:

Dim A = new MyClass("Something")
If A = "SomethingElse".ToMyClass()

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¹ LINQ to XML contains a bunch of rule-breaking design decisions which make it easier to use. This is an example of genius being able to trump normal good practice - but most of us don't have that level of genius.