From: bors <bors@rust-lang.org>
Date: Thu, 2 Nov 2017 00:06:16 +0000 (+0000)
Subject: Auto merge of #45306 - whitequark:ref_slice, r=alexcrichton
X-Git-Url: https://git.lizzy.rs/?a=commitdiff_plain;h=d5b69d4670dc5c1e3a095b1112f9496cd84462ab;hp=2be4cc040211a85b17f21e813ff62351ae4de642;p=rust.git

Auto merge of #45306 - whitequark:ref_slice, r=alexcrichton

Bring back slice::ref_slice as slice::from_ref.

These functions were deprecated and removed in 1.5, but such simple
functionality shouldn't require using unsafe code, and it isn't
cluttering libstd too much.

The original removal was quite contentious (see #27774), since then
we've had precedent for including such nuggets of functionality (see rust-lang/rfcs#1789),
and @nikomatsakis has provided a lot of use cases in https://github.com/rust-lang/rfcs/pull/1789#issuecomment-314640034.
Hence this PR.

I'm not too sure what to do with stability, feel free to correct me.
It seems pointless to go through stabilization for these functions though.

cc @aturon
---

diff --git a/src/liballoc/lib.rs b/src/liballoc/lib.rs
index 0cbfc9e9dac..f654a6b5ba4 100644
--- a/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@ -93,6 +93,7 @@
 #![feature(dropck_eyepatch)]
 #![feature(exact_size_is_empty)]
 #![feature(fmt_internals)]
+#![feature(from_ref)]
 #![feature(fundamental)]
 #![feature(fused)]
 #![feature(generic_param_attrs)]
diff --git a/src/liballoc/slice.rs b/src/liballoc/slice.rs
index 2045d5ddd97..0c5fec2cf74 100644
--- a/src/liballoc/slice.rs
+++ b/src/liballoc/slice.rs
@@ -119,6 +119,8 @@
 pub use core::slice::{RSplit, RSplitMut};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::slice::{from_raw_parts, from_raw_parts_mut};
+#[unstable(feature = "from_ref", issue = "45703")]
+pub use core::slice::{from_ref, from_ref_mut};
 #[unstable(feature = "slice_get_slice", issue = "35729")]
 pub use core::slice::SliceIndex;
 
diff --git a/src/libcore/slice/mod.rs b/src/libcore/slice/mod.rs
index 5039bef631e..57e5ae28664 100644
--- a/src/libcore/slice/mod.rs
+++ b/src/libcore/slice/mod.rs
@@ -2450,6 +2450,22 @@ pub unsafe fn from_raw_parts_mut<'a, T>(p: *mut T, len: usize) -> &'a mut [T] {
     mem::transmute(Repr { data: p, len: len })
 }
 
+/// Converts a reference to T into a slice of length 1 (without copying).
+#[unstable(feature = "from_ref", issue = "45703")]
+pub fn from_ref<T>(s: &T) -> &[T] {
+    unsafe {
+        from_raw_parts(s, 1)
+    }
+}
+
+/// Converts a reference to T into a slice of length 1 (without copying).
+#[unstable(feature = "from_ref", issue = "45703")]
+pub fn from_ref_mut<T>(s: &mut T) -> &mut [T] {
+    unsafe {
+        from_raw_parts_mut(s, 1)
+    }
+}
+
 // This function is public only because there is no other way to unit test heapsort.
 #[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "0")]
 #[doc(hidden)]