From a06f7f84e79ffa1f30c8c0add9310d0655540d91 Mon Sep 17 00:00:00 2001
From: Markus Everling <markuseverling@gmail.com>
Date: Tue, 29 Nov 2022 23:13:36 +0100
Subject: [PATCH] Add O(1) `Vec -> VecDeque` conversion guarantee

---
 library/alloc/src/collections/vec_deque/mod.rs | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/library/alloc/src/collections/vec_deque/mod.rs b/library/alloc/src/collections/vec_deque/mod.rs
index eab839e563e9f..2c8b975ca597a 100644
--- a/library/alloc/src/collections/vec_deque/mod.rs
+++ b/library/alloc/src/collections/vec_deque/mod.rs
@@ -2789,9 +2789,9 @@ impl<T, A: Allocator> From<Vec<T, A>> for VecDeque<T, A> {
     /// [`Vec<T>`]: crate::vec::Vec
     /// [`VecDeque<T>`]: crate::collections::VecDeque
     ///
-    /// In its current implementation, this is a very cheap
-    /// conversion. This isn't yet a guarantee though, and
-    /// shouldn't be relied on.
+    /// This conversion is guaranteed to run in *O*(1) time
+    /// and to not re-allocate the `Vec`'s buffer or
+    /// allocate any additional memory.
     fn from(other: Vec<T, A>) -> Self {
         let (ptr, len, cap, alloc) = other.into_raw_parts_with_alloc();
         Self { head: 0, len, buf: unsafe { RawVec::from_raw_parts_in(ptr, cap, alloc) } }