Returning Array Fragments - c#-3.0

Question

I need to get array fragments from an array. I'm sick of using Array.Copy().
new ArraySegment(..).Array returns the original [full] array. The one below is what I came up with but I feel it's pretty lame. Is there a better way to do this?
class Program
{
static void Main(string[] args)
{
var arr = new ArraySegment<byte>(new byte[5] { 5, 4, 3, 2, 1 }, 0, 2).ArrayFragment();
for (int i = 0; i < arr.Length; i++)
Console.WriteLine(i);
Console.Read();
}
}
static class Extensions
{
public static T[] ArrayFragment<T>(this ArraySegment<T> segment)
{
var arr = new T[segment.Count];
Array.Copy(segment.Array, segment.Offset, arr, 0, segment.Count);
return arr;
}
}
Thanks in advance.
Update:
The above was just an example.
I have a method: byte [] CalculateXXX(byte [] key, byte [] message);
I do array manipulations inside this method. I want to return portion of an array.
ArraySegment does not implement IEnumerable and it does NOT return an array with just the segment new ArraySegment(arr...).Array returns the complete original array.
var rval = new byte[4];
//new ArraySegment(finalOutputBuffer, 0, 4).SegmentedArray();
Array.Copy(finalOutputBuffer, 0, rval, 0, 4);
I find I had to do the above to return a array fragment. Was just wondering if there's a better way of returning fragments of an array [as new array].

Answer 1

Vyas, I am truly sorry for having posted this useless pile of ****. It's been ages since I've actually used ArraySegment and I simply assumed that it implemented a (more or less) consistent interface. Someone (Jon?) please tell me which drugs were used during the implementation of this useless struct.
Finally, to make a long story short, the best solution is probably to implement your own version of ArraySegment, only doing it right.
I don't understand your problem with using ArraySegment. There's no additional overhead involved here, if that's what you mean, since no copying of the original data is done. Rather, ArraySegment offers a lightweight view on the data.
Th make this work, change your (return) type from T[] to IEnumerable<T>, or, if you need indexed access, to IList<T>. Generally prefer using interface types in method signatures, and completely avoid array types. The rationale is very simple: it makes problems such as yours go away and makes the interface more flexible and future-proof. It also provides better information hiding since it hides parts of the implementation which aren't relevant for the consumer of this method.

Answer 2

Define better. What is the downside with ArraySegment? What problem are you having that it doesn't solve?
Edit: Ok, I now understand your point of view, but this is wrong. It might be a bug in the sense that you feel it should do more, but it does exactly what it is supposed to do. It allows you to pass information to a piece of code about an array you wish to use, and which portion of the array to use.
It doesn't provide IEnumerable or anything that gives you a narrow view of the array, ie. x[0] doesn't give you the first element of the segment, nor can you foreach over it.
So yes, it's rather useless on its own, but you wouldn't be able to get something that is an array at heart, and yet is also a segment of a larger array.
You could easily make your own collection-like class that references an array and uses the array as storage, and provides indexing, enumeration, etc.
But that's not what this structure does. I guess the main problem here is that they made you expect more from it through its name.

Answer 3

Just another side-effect of poor iterator design in C# btw. There are many instances similar (just as 'lame') where it would just plain good design to be able to pass or point or control segments (aka concept called range) without all the archane shickanery.. copy semantics or not, array is also a well-defined concept.
Just use C++. :-)