Question

I’m not sure if this is a strange thing to do or not, or if it is some how code smell…but I was wondering if there was a way (some sort of oop pattern would be nice) to ‘cast’ a base type to a form of its derived type. I know this makes little sense as the derived type will have additional functionality that the parent doesn’t offer which is in its self not fundamentally sound. But is there some way to do this? Here is a code example to so I can better explain what I’m asking.

public class SomeBaseClass {     public string GetBaseClassName {get;set;}     public bool BooleanEvaluator {get;set;} }  public class SomeDerivedClass : SomeBaseClass {     public void Insert(SqlConnection connection) {           //...random connection stuff           cmd.Parameters['IsItTrue'].Value = this.BooleanEvalutar;           //...     } }  public static void Main(object[] args) {     SomeBaseClass baseClass = new SomeBaseClass();     SomeDerivedClass derClass = (SomeDerivedClass)baseClass;      derClass.Insert(new sqlConnection()); } 

I know this seems goofy but is there any way to accomplish something of this sort?

Answer 1

Not soundly, in ‘managed’ languages. This is downcasting, and there is no sane down way to handle it, for exactly the reason you described (subclasses provide more than base classes – where does this ‘more’ come from?). If you really want a similar behaviour for a particular hierarchy, you could use constructors for derived types that will take the base type as a prototype.

One could build something with reflection that handled the simple cases (more specific types that have no addition state). In general, just redesign to avoid the problem.

Edit: Woops, can’t write conversion operators between base/derived types. An oddity of Microsoft trying to ‘protect you’ against yourself. Ah well, at least they’re no where near as bad as Sun.