I'm a web dev, mostly frontend, who just wants to make a macOS desktop app for fun. I know most of app development is on iOS these days, but I don't particularly like that platform and would rather focus on the desktop, if there's a difference. I've previously learned React, JS, PHP, Perl, and Visual Basic.
Not really interested in React Native or other similar JS-to-native frameworks. I want to make a lean, fast, simple and unbloated app with native look & feel.
That covers the language and the standard library. With your experience, reading that language ‘spec’ shouldn’t take more than a day (I think it’s a bit too loose to call it a spec, but that makes for a quicker read. It also may be that it is covering all edge cases, but so well written that it doesn’t look that way gedijt: just noticed there’s a “language reference” section now. IMO, that makes this (closer to) a spec)
As with most languages, getting a grip of the standard library, and learning to use it well will take more time.
There's also this course on Udacity (https://www.udacity.com/course/ios-developer-nanodegree--nd0...), in which you are exposed to some APIs (To use them) almost to the end (Since you have mentioned being interested in the networking capabilities available).
Hope that helps!
It's not expensive, nor is it free. Good stuff.