But macOS and iOS share enormous amounts of code, if not the majority. The kernel is pretty much the same. APIs usually get support on both systems, with the ex

But macOS and iOS share enormous amounts of code, if not the majority. The kernel is pretty much the same. APIs usually get support on both systems, with the exception being the UI layer. Indeed, if they have different APIs on the 2 platforms for the same functionality, you can probably bet that pretty soon one will be ported across to the other and the other obsoleted. Recent examples: PDFs, Bluetooth, Media SDKs (AV Foundation etc).