combine byte array using reduce

ReduceUsage.swift

import Foundation 

extension ExpressibleByIntegerLiteral {
    var bytes: [UInt8] { return withUnsafeBytes(of: self) { Array($0) } }
}

var id = UInt8(exactly: 1)!
var count = UInt8(exactly: 2)!
var timeStart = UInt64(exactly: 0x1234567898765432)!
var timeEnd = UInt64(exactly: 4)!
var size = UInt32(exactly: 5)!

let packet = [timeStart.bigEndian.bytes, timeEnd.bigEndian.bytes, size.bigEndian.bytes].reduce([id, count], +)

print(packet)