From fcee4656923a1128d0a2faf781242ee2d7835db4 Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Wed, 19 Dec 2018 12:00:42 -0800
Subject: [PATCH] Add a comment about memory management

---
 examples/request-animation-frame/src/lib.rs | 49 +++++++++++++--------
 1 file changed, 30 insertions(+), 19 deletions(-)

diff --git a/examples/request-animation-frame/src/lib.rs b/examples/request-animation-frame/src/lib.rs
index fd83b6843..81def4c63 100644
--- a/examples/request-animation-frame/src/lib.rs
+++ b/examples/request-animation-frame/src/lib.rs
@@ -26,31 +26,42 @@ fn body() -> web_sys::HtmlElement {
 // This function is automatically invoked after the wasm module is instantiated.
 #[wasm_bindgen(start)]
 pub fn run() -> Result<(), JsValue> {
+    // Here we want to call `requestAnimationFrame` in a loop, but only a fixed
+    // number of times. After it's done we want all our resources cleaned up. To
+    // achieve this we're using an `Rc`. The `Rc` will eventually store the
+    // closure we want to execute on each frame, but to start out it contains
+    // `None`.
+    //
+    // After the `Rc` is made we'll actually create the closure, and the closure
+    // will reference one of the `Rc` instances. The other `Rc` reference is
+    // used to store the closure, request the first frame, and then is dropped
+    // by this function.
+    //
+    // Inside the closure we've got a persistent `Rc` reference, which we use
+    // for all future iterations of the loop
     let f = Rc::new(RefCell::new(None));
     let g = f.clone();
 
-    {
-        let mut i = 0;
-        *g.borrow_mut() = Some(Closure::wrap(Box::new(move || {
-            if i > 300 {
-                body().set_text_content(Some("All done!"));
+    let mut i = 0;
+    *g.borrow_mut() = Some(Closure::wrap(Box::new(move || {
+        if i > 300 {
+            body().set_text_content(Some("All done!"));
 
-                // Drop our handle to this closure so that it will get cleaned
-                // up once we return.
-                let _ = f.borrow_mut().take();
-                return;
-            }
+            // Drop our handle to this closure so that it will get cleaned
+            // up once we return.
+            let _ = f.borrow_mut().take();
+            return;
+        }
 
-            // Set the body's text content to how many times this
-            // requestAnimationFrame callback has fired.
-            i += 1;
-            let text = format!("requestAnimationFrame has been called {} times.", i);
-            body().set_text_content(Some(&text));
+        // Set the body's text content to how many times this
+        // requestAnimationFrame callback has fired.
+        i += 1;
+        let text = format!("requestAnimationFrame has been called {} times.", i);
+        body().set_text_content(Some(&text));
 
-            // Schedule ourself for another requestAnimationFrame callback.
-            request_animation_frame(f.borrow().as_ref().unwrap());
-        }) as Box<FnMut()>));
-    }
+        // Schedule ourself for another requestAnimationFrame callback.
+        request_animation_frame(f.borrow().as_ref().unwrap());
+    }) as Box<FnMut()>));
 
     request_animation_frame(g.borrow().as_ref().unwrap());
     Ok(())