C# - Can I use an array initializer to build one b

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

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});
}

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

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 });