C# - Can I use an array initializer to build one byte array out of another?

Question

I'd like to use an array initializer to build one byte array out of another byte array as well as some other bytes that form a header/trailer. Basically, I'd like to do something like this:

byte[] DecorateByteArray(byte[] payload)
{
    return new byte[] { 0, 1, 2, payload.GetBytes(), 3, 4, 5};
}

GetBytes() above is fictional, unfortunately.

Is there any nice/elegant way to do this? I solved this by using a BinaryWriter to write everything to a MemoryStream, and then converting this into a byte array with MemoryStream.ToArray(), but it feels kind of clunky.

Answer 1

The closest you could get would be:

byte[] DecorateByteArray(byte[] payload) =>
    new byte[] { 0, 1, 2 } 
       .Concat(payload)
       .Concat(new byte[] { 3, 4, 5 })
       .ToArray();

That would be pretty inefficient though. You'd be better off doing something like:

static T[] ConcatArrays<T>(params T[][] arrays)
{
    int length = arrays.Sum(a => a.Length);
    T[] ret = new T[length];
    int offset = 0;
    foreach (T[] array in arrays)
    {
        Array.Copy(array, 0, ret, offset, array.Length);
        offset += array.Length;
    }
    return ret;
}

(Consider using Buffer.BlockCopy too, where appropriate.)

Then call it with:

var array = ConcatArrays(new byte[] { 0, 1, 2 }, payload, new byte[] { 3, 4, 5 });

Answer 2

You can create a new collection that is a List<byte>, but that has an overload of Add that adds a whole array of bytes:

public class ByteCollection: List<byte>
{
    public void Add(IEnumerable<byte> bytes)
    {
        AddRange(bytes);
    }
}

This then lets you use the collection initializer for this type to supply either a single byte or a sequence of bytes, which you can then turn back into an array if you need an array:

byte[] DecorateByteArray(byte[] payload)
{
    return new ByteCollection() { 0, 1, 2, payload, 3, 4, 5 }.ToArray();
}

Answer 3

One easy way is to break out each into parts and then concat them

byte[] DecorateByteArray(byte[] payload)
{  
    return new byte[] { 0, 1, 2}
        .Concat(payload.GetBytes())
        .Concat(new byte[] { 3, 4, 5});
}