Update alloc.rs

[rust.git] / src / libcore / alloc.rs

diff --git a/src/libcore/alloc.rs b/src/libcore/alloc.rs
index f3a2b73f2b8de92d3d6299ec0db48c853d2ec3db..0a7a8ab266aee9986f59cfafa65e91259d2ef6eb 100644 (file)
--- a/src/libcore/alloc.rs
+++ b/src/libcore/alloc.rs
@@ -140,6 +140,18 @@ pub fn for_value<T: ?Sized>(t: &T) -> Self {
         unsafe { Layout::from_size_align_unchecked(size, align) }
     }
 
+    /// Creates a `NonNull` that is dangling, but well-aligned for this Layout.
+    ///
+    /// Note that the pointer value may potentially represent a valid pointer,
+    /// which means this must not be used as a "not yet initialized"
+    /// sentinel value. Types that lazily allocate must track initialization by
+    /// some other means.
+    #[unstable(feature = "alloc_layout_extra", issue = "55724")]
+    pub const fn dangling(&self) -> NonNull<u8> {
+        // align is non-zero and a power of two
+        unsafe { NonNull::new_unchecked(self.align() as *mut u8) }
+    }
+
     /// Creates a layout describing the record that can hold a value
     /// of the same layout as `self`, but that also is aligned to
     /// alignment `align` (measured in bytes).