Question

LinQ contains the method Cast which casts each entry in the list to type T. Lets say we have a list which looks like the following:

List<Object> obj = new List<Object>();
obj.Add("A");
obj.Add("B");

A working cast could be

var list = obj.Cast<string>();

What I would like to work

Type t = typeof(String);
Object list = obj.Cast(t);

A solution would be to use reflection and genericly create a list and populate it but I was wondering if there exist any better solution? Heard that .NET 4.0 should support some co/contra-variance which may be a way to do it.

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Extra Information and Reflection Soulution

The error I get is the following The model item passed into the dictionary is of type System.Collections.Generic.List1[IStatisticEntry], but this dictionary requires a model item of type System.Collections.Generic.List1[CrashStatistic+CrashEntry].
Note that CrashEntry implements IStaticEntry but cannot be casted because it is a generic type of the list.

I constructed the following solution through I would stille like something without Reflection:

    public static object Cast(this IEnumerable list, Type type)
    {
        var newList = Activator.CreateInstance(typeof(List<>).MakeGenericType(type));

        foreach (var item in list)
            newList.GetType().GetMethod("Add").Invoke(newList, new object[] { item });

        return newList;
    }

Answer 1

It’s not possible to do this statically, any more than you can do it with a single object.

Type t = typeof(string);
var x = (t)obj; // invalid

However, it is possible to treat the elements dynamically so that a cast to the underlying type isn’t necessary:

static void Main(string[] args)
{
    List<Object> obj = new List<Object>();
    obj.Add("A");
    obj.Add("B");

    var list = obj.Cast<dynamic>();
    foreach (var item in list)
    {
        Console.WriteLine(item[0]);
    }

    Console.ReadKey();
}