From 9425e304b13e5cfc6f5d36f0a872fc8313da40aa Mon Sep 17 00:00:00 2001
From: Caleb Sander <caleb.sander@gmail.com>
Date: Mon, 28 Dec 2020 15:45:36 -0500
Subject: [PATCH] Avoid unnecessary Vec construction in BufReader

---
 library/std/src/io/buffered/bufreader.rs | 7 +++----
 library/std/src/lib.rs                   | 1 +
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/library/std/src/io/buffered/bufreader.rs b/library/std/src/io/buffered/bufreader.rs
index 987371f50ec22..152bd34ffbaf2 100644
--- a/library/std/src/io/buffered/bufreader.rs
+++ b/library/std/src/io/buffered/bufreader.rs
@@ -90,10 +90,9 @@ impl<R: Read> BufReader<R> {
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn with_capacity(capacity: usize, inner: R) -> BufReader<R> {
         unsafe {
-            let mut buffer = Vec::with_capacity(capacity);
-            buffer.set_len(capacity);
-            inner.initializer().initialize(&mut buffer);
-            BufReader { inner, buf: buffer.into_boxed_slice(), pos: 0, cap: 0 }
+            let mut buf = Box::new_uninit_slice(capacity).assume_init();
+            inner.initializer().initialize(&mut buf);
+            BufReader { inner, buf, pos: 0, cap: 0 }
         }
     }
 }
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index ba49dee38e642..f62fb83533ca2 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -289,6 +289,7 @@
 #![feature(needs_panic_runtime)]
 #![feature(negative_impls)]
 #![feature(never_type)]
+#![feature(new_uninit)]
 #![feature(nll)]
 #![feature(nonnull_slice_from_raw_parts)]
 #![feature(once_cell)]