Question

So lets say I have a class like

public class Complex { } // this is what I mean when I say List<Complex>
// its just a user-defined class or type if you will

Now let’s say I have a method which returns a list that holds objects.

Now let’s say I can further guarantee that each of these objects in the list is actually of type Complex (in other words List < Complex >)

I would like the most painless way of casting this list as possible. A one-liner would be ideal, but a few lines would be fine too.

Here is what I tried (but doesn’t work – InvalidCastOperation exception):

// Sorry this is so hard to read! Also .Cast<Complex>() doesn't work either :(

return (ComplexCollection) ((List<Complex>) ((List<object>) complexElementsDictionary["ComplexElementCollection"]).OfType<Complex>()); 

Some specifics about this code snippet:

ComplexCollection inherits List<Complex>
complexElementsDictionary is of type (Dictionary<string, List<object>)

So in plain terms I’m asking a Dictionary<> for its corresponding list of objects. Then I try to cast this list to what its supposed to be, which is a list of Complex.

Note – Please try to ignore the fact that I am casting like this at runtime. I’m deserializing an XML collection (in app.config actually) and this is how I’ve chosen to do it. There may be a better way, but for now I just want to see if anyone knows a way to do what I’m asking.

Thank you so much! I hope it is clear what I’m asking, and if not I’ll update the question.

Answer 1

To convert a List<object> to List<Complex> is as simple as:

List<object> objectList = complexElementsDictionary["ComplexElementCollection"];
List<Complex> complexList = objectList.Cast<Complex>().ToList();

However you can’t cast a List<Complex> to ComplexCollection just because ComplexCollection inherits from List<Complex>. (the other way around is fine though)

List<T> has a constructor which takes an IEnumerable<T> and adds the elements to a list. So I think what you need is to add this constructor to ComplexCollection:

public ComplexCollection(IEnumerable<Complex> values) : base(values)
{
    /* plus any other logic you have */
}

And then your example with the return statement becomes:

return new ComplexCollection(
    complexElementsDictionary["ComplexElementCollection"].Cast<Complex>()
);