From e132f0bc8e7ac08cad0f2e2cdd55841d0576cf61 Mon Sep 17 00:00:00 2001
From: Alexis Beingessner <a.beingessner@gmail.com>
Date: Fri, 19 Jun 2015 13:55:01 -0700
Subject: [PATCH] add note for future type-system adventurers

---
 src/libcore/ptr.rs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/libcore/ptr.rs b/src/libcore/ptr.rs
index 31cdb6093c8..f2792a525d6 100644
--- a/src/libcore/ptr.rs
+++ b/src/libcore/ptr.rs
@@ -512,6 +512,11 @@ impl<T: ?Sized> PartialOrd for *mut T {
 #[unstable(feature = "unique", reason = "needs an RFC to flesh out design")]
 pub struct Unique<T: ?Sized> {
     pointer: NonZero<*const T>,
+    // NOTE: this marker has no consequences for variance, but is necessary
+    // for dropck to understand that we logically own a `T`.
+    //
+    // For details, see:
+    // https://github.com/rust-lang/rfcs/blob/master/text/0769-sound-generic-drop.md#phantom-data
     _marker: PhantomData<T>,
 }