feat: add async fn

__concurrent/async-fn-resumed-after-completion/src/main.rs

@@ -0,0 +1,48 @@
+async fn action(input: Option<i32>) -> Option<String> {
+    // 若 input（输入）是None，则返回 None
+    // 事实上也可以这么写: `let i = input?;`
+    let _i = match input {
+        Some(input) => input,
+        None => return None,
+    };
+
+    // 这里定义一些逻辑
+    Some("test".into())
+}
+
+#[tokio::main]
+async fn main() {
+    let (tx, mut rx) = tokio::sync::mpsc::channel(128);
+
+    let mut done = false;
+    let operation = action(None);
+    tokio::pin!(operation);
+
+    tokio::spawn(async move {
+        let _ = tx.send(1).await;
+        let _ = tx.send(3).await;
+        let _ = tx.send(2).await;
+    });
+
+    loop {
+        tokio::select! {
+            res = &mut operation, if !done => {
+                println!("res = &mut operation, done={}", done);
+                done = true;
+
+                if let Some(v) = res {
+                    println!("GOT = {}", v);
+                    return;
+                }
+            }
+            Some(v) = rx.recv() => {
+                println!("Some(v={}) = rx.recv()", v);
+                if v % 2 == 0 {
+                    // `.set` 是 `Pin` 上定义的方法
+                    operation.set(action(Some(v)));
+                    done = false;
+                }
+            }
+        }
+    }
+}