Question

I am trying to accomplish something in C# that I do easily in Java. But having some trouble.
I have an undefined number of arrays of objects of type T.
A implements an interface I.
I need an array of I at the end that is the sum of all values from all the arrays.
Assume no arrays will contain the same values.

This Java code works.

ArrayList<I> list = new ArrayList<I>();
for (Iterator<T[]> iterator = arrays.iterator(); iterator.hasNext();) {
    T[] arrayOfA = iterator.next();
    //Works like a charm
    list.addAll(Arrays.asList(arrayOfA));
}

return list.toArray(new T[list.size()]);

However this C# code doesn’t:

List<I> list = new List<I>();
foreach (T[] arrayOfA in arrays)
{
    //Problem with this
    list.AddRange(new List<T>(arrayOfA));
    //Also doesn't work
    list.AddRange(new List<I>(arrayOfA));
}
return list.ToArray();

So it’s obvious I need to somehow get the array of T[] into an IEnumerable<I> to add to the list but I’m not sure the best way to do this? Any suggestions?

EDIT: Developing in VS 2008 but needs to compile for .NET 2.0.

Answer 1

The issue here is that C# doesn’t support co-variance (at least not until C# 4.0, I think) in generics so implicit conversions of generic types won’t work.

You could try this:

List<I> list = new List<I>();
foreach (T[] arrayOfA in arrays)
{
    list.AddRange(Array.ConvertAll<T, I>(arrayOfA, t => (I)t));
}
return list.ToArray();

---

For anyone that strumbles across this question and is using .NET 3.5, this is a slightly more compact way of doing the same thing, using Linq.

List<I> list = new List<I>();
foreach (T[] arrayOfA in arrays)
{
    list.AddRange(arrayOfA.Cast<I>());
}
return list.ToArray();