Converting List<object> to List<complex> where complex is a user-defined type

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 开发者_开发百科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.

Breaking up your example code and modifying it slightly to use Cast():

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

You now have a list of objects of the required type. But what you actually want is an instance of your collection object, and this cannot be obtained by another cast. That is, you can't do this:

ComplexCollection collection = (ComplexCollection)typedList;

because typedList simply isn't an instance of ComplexCollection and there is no conversion operator available to the compiler to convert from List<Complex> to ComplexCollection.

You will need to create your instance and add the Complex objects to it:

ComplexCollection collection = new ComplexCollection();
foreach(Complex c in typedList){
    collection.Add(c);
}

Or in just four lines:

ComplexCollection collection = new ComplexCollection();
foreach(Complex c in complexElementsDictionary["ComplexElementCollection"].Cast<>(Complex)){
    collection.Add(c);
}

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>()
);

To convert a list to a new type you can just do something as simple as

(ComplexCollection)(yourList.Select(x => (complexType)x).ToList());

That should work, basically your going through your list of objects in the dictionary and casting each item to the appropriate type, then converting that to a list and then converting your list to the more specific collection type.

I'm afried there's no direct solution. Maybe you could use ConvertAll:

// ol is of type List<Object>
List<Complex> cl = ol.ConvertAll(o=>(Complex)c);