add an example with async_trait

Cargo.toml

@@ -28,3 +28,5 @@ proc-macro-error = "1.0.0"
 
 [dev-dependencies]
 trybuild = "1"
+async-trait = "0.1"
+async-std = { version = "1", features = ["attributes"] }

examples/async_trait.rs

@@ -0,0 +1,32 @@
+use std::time::Duration;
+use async_std::task;
+
+use async_trait::async_trait;
+use auto_impl::auto_impl;
+
+// Note the order of the attributes here:
+// `#[async_trait]` must appear first
+#[async_trait]
+#[auto_impl(&, Box, Arc)]
+trait Component {
+    async fn run(&self);
+}
+
+struct WaitABit(Duration);
+
+#[async_trait]
+impl Component for WaitABit {
+    async fn run(&self) {
+        task::sleep(self.0).await;
+    }
+}
+
+async fn run_async(a: impl Component) {
+    a.run().await;
+}
+
+#[async_std::main]
+async fn main() {
+    // We can treat our `Box<WaitABit>` as an `impl Component` directly
+    run_async(Box::new(WaitABit(Duration::from_secs(1)))).await;
+}