> I don’t know about anyone else, but at least for me, when I’m building a new feature I usually don’t have all the data types, APIs, and other fine details worked out up front. I’m often just farting out code trying to get some basic idea working and checking whether my assumptions about how things should work are more-or-less correct. Doing this in, say, Python is extremely easy, because you can play fast and loose with things like typing and not worry if certain code paths are broken while you rough out your idea. You can go back later and make it all tidy and fix all the type errors and write all the tests.
> In Rust, this kind of “draft coding” is very difficult, because the compiler can and will complain about every goddamn thing that does not pass type and lifetime checking — as it is explicitly designed to do. This makes perfect sense when you need to build your final, production-ready implementation, but absolutely sucks when you’re trying to cruft something together to test an idea or get a basic foundation in place. The unimplemented! macro is helpful to a point, but still requires that everything typechecks up and down the stack before you can even compile.
This rings so true for me. I could "mock up" entire apps using interfaces in Java, without having to actually write impl code. I could be sloppy as hell around the edges, but that didn't matter, because I could get the large design right without the compiler screaming.
In Rust, there is the chasm between no code and anything that works, feels so draggy.
But it is not absurd. Facebook doesn't target ads at you, Bob Jones.
It takes all of Bob's activities and pushes them into bins based on how they characterize Bob; Male, lives in Iowa, 18-25, etc. a bin (Moves to LA, for example), his data will contribute to different bins. This activity is disconnected from Bob at this point; and the data is aggregated away from single interaction events. "Bob visited foo.com" as a single event is gone at this point.
The models grind on these aggregate data bins.
Then when ads are targeted at Males who live in Iowa, aged 18-25 -- those ads get shown to Bob, because he is tagged with those tags.
They don't "keep track of which webpages you visit", not for more than a day. Those events get pushed in large aggregate stores of activities pretty fast. These aggregate stores are vastly smaller than if you kept all the individual data, hence much cheaper.