# Joins an array of bytes `arr` separated by `sep`
#
#     assert join_bytes(["String".to_bytes, "is".to_bytes, "string".to_bytes], u' ').hexdigest == "537472696E6720697320737472696E67"
fun join_bytes(arr: Array[Bytes], sep: nullable BytePattern): Bytes do
	if arr.is_empty then return new Bytes.empty
	sep = sep or else new Bytes.empty
	var endln = sep.pattern_length * (arr.length - 1)
	for i in arr do endln += i.length
	var ret = new Bytes.with_capacity(endln)
	ret.append(arr.first)
	for i in  [1 .. arr.length[ do
		sep.append_to(ret)
		ret.append arr[i]
	end
	return ret
end