I am trying to find the fastest way to return a part of an array in C# My current way is as follows:
// .. set int moveCount ..
// .. set int[] childArray ..
int[] realArray = new int[moveCount];
Array.Copy(childArray, realArray, moveCount);
return realArray;
This is the way I see it everywhere on the net, but I wonder if the array will be copied twice now. Once because I do it, and once because of returning.
No, when you return you'll be returning a reference to the array you've just created. The reference will be copied, but that's dirt cheap.
All arrays are reference types, even if the element type of the array is a value type (so int[] is a reference type even though int is a value type).
Now you could still consider returning ArraySegment<int> instead of int[] - that way you wouldn't end up copying any values within the array. On the other hand, if the original array is changed, those changes will affect what the caller sees (and likewise the caller can change the array contents).
No, your assumption is wrong, your return statement returns a reference to the created array. So no, you are not creating two copies of the array returned. For the part regarding the block copy, I think that your Array.Copy is the best tradeoff.
If sounds like you want to use LINQ Take:
return realArray.Take(numberOfItems);
Note: This works for taking the first to N elements in the array
IEnumerable<int> instead of an int[], so you can't access it like an array, only loop through it.