Add Option::as_pin_mut

Author: cramertj

src/libcore/lib.rs

@@ -74,6 +74,7 @@
 #![deny(missing_debug_implementations)]
 
 #![feature(allow_internal_unstable)]
+#![feature(arbitrary_self_types)]
 #![feature(asm)]
 #![feature(associated_type_defaults)]
 #![feature(attr_literals)]

src/libcore/option.rs

@@ -147,6 +147,7 @@
 
 use iter::{FromIterator, FusedIterator, TrustedLen};
 use {mem, ops};
+use mem::PinMut;
 
 // Note that this is not a lang item per se, but it has a hidden dependency on
 // `Iterator`, which is one. The compiler assumes that the `next` method of
@@ -269,6 +270,15 @@ impl<T> Option<T> {
         }
     }
 
+    /// Converts from `Option<T>` to `Option<PinMut<'_, T>>`
+    #[inline]
+    #[unstable(feature = "pin", issue = "49150")]
+    pub fn as_pin_mut<'a>(self: PinMut<'a, Self>) -> Option<PinMut<'a, T>> {
+        unsafe {
+            PinMut::get_mut(self).as_mut().map(|x| PinMut::new_unchecked(x))
+        }
+    }
+
     /////////////////////////////////////////////////////////////////////////
     // Getting to contained values
     /////////////////////////////////////////////////////////////////////////