# Async component
Zero overhead reactive programming
## Example
See `async_component/examples/example.rs` for simple example.
See `examples/gui-demo` project for example using with gui(winit, raqote, pixels).
### Code
```Rust
use async_component::AsyncComponent;
#[derive(Debug, AsyncComponent)]
struct CounterComponent {
// State must be wrapped with StateCell
#[state(Self::on_counter_update)]
counter: StateCell<i32>,
// Stream
// It iterates every queued items in single poll to prevent slowdown.
// If the stream is immediate and resolves indefinitely, the task will fall to infinite loop. See expanded code below.
#[state(Self::on_counter_recv)]
counter_recv: StreamCell<Receiver<i32>>,
}
impl CounterComponent {
fn on_counter_update(&mut self, _: ()) {
println!("Counter updated to: {}", *self.counter);
}
fn on_counter_recv(&mut self, counter: i32) {
*self.sub_component.counter = counter;
}
}
```
Running this component stream will print initial value first and print changed value if new values are sent through channel.
```
Counter updated to: 0
Counter updated to: ...
```