make Leptos iteration example equivalent of Dioxus iteration example (#2191)

README.md

@@ -270,61 +270,28 @@ fn Counters() -> Element {
 }
 ```
 
-[While in Leptos, you would need to track keys, use the `<For>` component, create new signals, and manually clean up memory](https://book.leptos.dev/view/04_iteration.html#dynamic-rendering-with-the-for-component):
+[While in Leptos you would use the `<For>` component.](https://book.leptos.dev/view/04_iteration.html#dynamic-rendering-with-the-for-component):
 
 ```rust
 fn Counters() -> Element {
-    let initial_counters = (0..initial_length)
-        .map(|id| (id, create_signal(id + 1)))
-        .collect::<Vec<_>>();
-
-    let (counters, set_counters) = create_signal(initial_counters);
-
-    let add_counter = move |_| {
-        let sig = create_signal(next_counter_id + 1);
-        set_counters.update(move |counters| counters.push((next_counter_id, sig)));
-        next_counter_id += 1;
-    };
+    let counters = RwSignal::new(vec![0; 10]);
 
     view! {
-        <div>
-            <button on:click=add_counter>
-                "Add Counter"
-            </button>
-            <ul>
+        <button on:click=move |_| counters.update(|n| n.push(n.len()))>"Add Counter"</button>
         <For
-                    each=counters
-                    key=|counter| counter.0
-                    children=move |(id, (count, set_count))| {
-                        view! {
+            each=move || 0..counters.with(Vec::len)
+            key=|idx| *idx
+            let:idx
+        >
             <li>
-                                <button
-                                    on:click=move |_| set_count.update(|n| *n += 1)
-                                >
-                                    {count}
+                <button on:click=move |_| counters.update(|n| n[idx] += 1)>
+                    {Memo::new(move |_| counters.with(|n| n[idx]))}
                 </button>
-                                <button
-                                    on:click=move |_| {
-                                        set_counters.update(|counters| {
-                                            counters.retain(|(counter_id, (signal, _))| {
-
-                                                if counter_id == &id {
-                                                    signal.dispose();
-                                                }
-                                                counter_id != &id
-                                            })
-                                        });
-                                    }
-                                >
+                <button on:click=move |_| counters.update(|n| { n.remove(idx); })>
                     "Remove"
                 </button>
             </li>
-                        }
-                    }
-                />
-            </ul>
-        </div>
-    }
+        </For>
     }
 ```