add generics example to actix-web

actix-web/examples/generics.rs

@@ -0,0 +1,34 @@
+use actix_web::{web, App, Error, HttpResponse, HttpServer, Result};
+
+async fn index<T: ApiProvider>(api: web::Data<T>) -> Result<HttpResponse, Error> {
+    let hi = api.dont_worry();
+    println!("{}", hi);
+
+    Ok(HttpResponse::Ok().body(hi))
+}
+
+pub trait ApiProvider {
+    fn dont_worry(&self) -> String;
+}
+
+pub struct Api {}
+
+impl ApiProvider for Api {
+    fn dont_worry(&self) -> String {
+        "be happy".to_string()
+    }
+}
+
+#[actix_web::main]
+async fn main() -> std::io::Result<()> {
+    let api = web::Data::new(Api {});
+
+    HttpServer::new(move || {
+        App::new()
+            .app_data(api.clone())
+            .service(web::resource("/").route(web::get().to(index::<Api>)))
+    })
+    .bind(("127.0.0.1", 8080))?
+    .run()
+    .await
+}