It's important to note that this new ad slot "will allow advertisers to promote their apps across the whole network, rather than in response to specific searches." This is exactly Facebook's game, and the underlying technology they use to target these ads could easily be repurposed for oh, I don't know...a new search engine?
Coincidentally, iOS 13 updated iBeacon in a way that also made it a lot less useful to developers (although there was a clear privacy benefit for users.)
I was doing academic research on this exact topic and Chris' is the only book that I found that breaks down the techniques one at a time this way. This book is nothing short of brilliant.
Right now I code two days a week and do academic/journalistic writing the other three days a week. The work styles are totally different.
With programming, I work at nearly full capacity until I'm almost done with the task, and then get sort of distracted during that last little bit of testing and documenting.
Writing I find far less conducive to a "flow" state though. I alternate pretty much the entire day between 30-60 minute chunks of working and 10-20 minute chunks walking outside or checking HN.
In the rare instances when I have to switch between the two modes, my productivity basically collapses.