I developed most of my iOS game without internet access (I did it mostly on a train). I actually did this twice - once using a Mac, xCode, swift, and spritekit

I developed most of my iOS game without internet access (I did it mostly on a train). I actually did this twice - once using a Mac, xCode, swift, and spritekit. Then the exact same app again using a Linux machine, text editor, C, and SDL2. Doing things in C was far better - I just opened up the relevant SDL header files when I needed information, and was able to get basically everything non-iOS specific up and running without any internet. I definitely drew on a fair bit of experience and hunches (e.g. writing audio synthesizers from scratch often involves picking a bunch of magic numbers, and if you pick them wrong it can sound completely awful). Now I have a mac laptop again, I still would lean towards C+SDL2 over swift+SpriteKit (though I do continue to experiment).