Avoid unnecessary Vec construction in BufReader

rust-lang · Mar 3, 2021 · 9425e30 · 9425e30
1 parent 939b143
commit 9425e30
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Showing 2 changed files with 4 additions and 4 deletions.
diff --git 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
@@ -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)]