Auto merge of #41437 - cuviper:remove-unstable-deprecated, r=alexcrichton

[rust.git] / src / liballoc / rc.rs

diff --git a/src/liballoc/rc.rs b/src/liballoc/rc.rs
index b12d89867c8efcac9ae1c1af0d73165eafc7b31b..38dc914583517f9410e1f685fbe0b50e47286ec6 100644 (file)
--- a/src/liballoc/rc.rs
+++ b/src/liballoc/rc.rs
@@ -239,7 +239,7 @@
 use core::ptr::{self, Shared};
 use core::convert::From;
 
-use heap::deallocate;
+use heap::{allocate, deallocate, box_free};
 use raw_vec::RawVec;
 
 struct RcBox<T: ?Sized> {
@@ -248,7 +248,6 @@ struct RcBox<T: ?Sized> {
     value: T,
 }
 
-
 /// A single-threaded reference-counting pointer.
 ///
 /// See the [module-level documentation](./index.html) for more details.
@@ -425,6 +424,38 @@ pub fn __from_str(value: &str) -> Rc<str> {
     }
 }
 
+impl<T> Rc<[T]> {
+    /// Constructs a new `Rc<[T]>` from a `Box<[T]>`.
+    #[doc(hidden)]
+    #[unstable(feature = "rustc_private",
+               reason = "for internal use in rustc",
+               issue = "0")]
+    pub fn __from_array(value: Box<[T]>) -> Rc<[T]> {
+        unsafe {
+            let ptr: *mut RcBox<[T]> =
+                mem::transmute([mem::align_of::<RcBox<[T; 1]>>(), value.len()]);
+            // FIXME(custom-DST): creating this invalid &[T] is dubiously defined,
+            // we should have a better way of getting the size/align
+            // of a DST from its unsized part.
+            let ptr = allocate(size_of_val(&*ptr), align_of_val(&*ptr));
+            let ptr: *mut RcBox<[T]> = mem::transmute([ptr as usize, value.len()]);
+
+            // Initialize the new RcBox.
+            ptr::write(&mut (*ptr).strong, Cell::new(1));
+            ptr::write(&mut (*ptr).weak, Cell::new(1));
+            ptr::copy_nonoverlapping(
+                value.as_ptr(),
+                &mut (*ptr).value as *mut [T] as *mut T,
+                value.len());
+
+            // Free the original allocation without freeing its (moved) contents.
+            box_free(Box::into_raw(value));
+
+            Rc { ptr: Shared::new(ptr as *const _) }
+        }
+    }
+}
+
 impl<T: ?Sized> Rc<T> {
     /// Creates a new [`Weak`][weak] pointer to this value.
     ///