From 91e88a4976cf4d61026a3ed8d7589cb18f8e9d18 Mon Sep 17 00:00:00 2001
From: bluss <bluss@users.noreply.github.com>
Date: Sun, 25 Nov 2018 16:33:07 +0100
Subject: [PATCH] FEAT: Simplify stack guard in extend

This simplification -- borrowing self.len instead of self, leads to
an improvement in the extend_from_slice benchmark.

It's also guided by the discussion of stacked borrows; the old code
would be invalid, because the whole self is borrowed while ptr is derived from
self.
---
 src/lib.rs | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 75860dd..fb40456 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -890,10 +890,10 @@ impl<A: Array> Extend<A::Item> for ArrayVec<A> {
             // We update the length to handle panic in the iteration of the
             // user's iterator, without dropping any elements on the floor.
             let mut guard = ScopeExitGuard {
-                value: self,
+                value: &mut self.len,
                 data: len,
-                f: |&len, self_| {
-                    self_.set_len(len)
+                f: move |&len, self_len| {
+                    **self_len = Index::from(len);
                 }
             };
             for elt in iter.into_iter().take(take) {