Hide the implementation detail of the extracted check.

Author: nk9

library/alloc/src/vec/mod.rs

@@ -3672,12 +3672,12 @@ impl<T, A: Allocator> Vec<T, A> {
     /// # let range = 1..5;
     /// let mut i = range.start;
     /// let end_items = vec.len() - range.end;
-    /// let mut extracted = vec![];
+    /// # let mut extracted = vec![];
     ///
     /// while i < vec.len() - end_items {
     ///     if some_predicate(&mut vec[i]) {
     ///         let val = vec.remove(i);
-    ///         extracted.push(val);
+    /// #         extracted.push(val);
     ///         // your code here
     ///     } else {
     ///         i += 1;