Cargo can't do nested workspaces.

examples/flexible-responders/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "flexible-responders"
+version = "0.1.0"
+edition = "2018"
+
+[dependencies]
+actix-web = "1.0"
+serde = "1.0"

examples/flexible-responders/src/main.rs

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+use actix_web::{web, App, HttpRequest, HttpServer, Responder};
+use serde::Serialize;
+
+// <flexible-responders>
+#[derive(Serialize)]
+struct Measurement {
+    temperature: f32,
+}
+
+fn hello_world() -> impl Responder {
+    "Hello World!"
+}
+
+fn current_temperature(_req: HttpRequest) -> impl Responder {
+    web::Json(Measurement { temperature: 42.3 })
+}
+
+fn main() {
+    HttpServer::new(|| {
+        App::new()
+            .service(web::resource("/").to(hello_world))
+            .service(web::resource("/temp").to(current_temperature))
+    })
+    .bind("127.0.0.1:8088")
+    .unwrap()
+    .run()
+    .unwrap();
+}
+// </flexible-responders>