The name 'drying_paint' comes from the expression "watching paint dry". This module provides a system to "watch" some values for changes and run code whenever they change.

The typical usage is as follows: you first define a structure to hold data, including some "watched" data.

rust struct HelloData { name: Watched<String>, greeting: String, }

Implementing the trait WatcherInit for that structure gives you an place to set-up the code that should run when a watched value changes.

rust impl WatcherInit for HelloData { fn init(watcher: &mut WatcherMeta<Self>) { watcher.watch(|root| { root.greeting = format!("Hello, {}!", root.name); }); } }

Normally you need to wrap the data struct in a Watcher, so it's common to alias the watcher type to cleanup the syntax a bit: rust type Hello = Watcher<HelloData>; Creating watchers and setting watched data needs to happen within a WatchContext. WatchContext::update_current() will cause all the pending watcher code to run.

rust fn main() { let mut ctx = WatchContext::new(); ctx.with(|| { let mut obj = Hello::new(); *obj.data_mut().name = "Rust".to_string(); WatchContext::update_current(); assert_eq!(obj.data().greeting, "Hello, Rust!"); }); }