When you're a developer you really end up specializing in one particular set of what we call APIs. So I have a lot of experience professionally as an iOS developer. And so I am pretty good at making iOS apps but I'm not as big an expert on making Android apps. To be as good an Android developer as I am an iOS developer would take years of work and experience to get to that level. On the iOS side the vast majority of developers at this point have moved from Objective C to Swift. A lot of people have moved forward to Kotlin which is a modern programming language developed by JetBrains.