alloc: impl fmt::Pointer for Rc, Arc and Box

Closes rust-lang#24091

Author: richo

src/liballoc/arc.rs

@@ -668,6 +668,13 @@ impl<T: fmt::Debug> fmt::Debug for Arc<T> {
     }
 }
 
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> fmt::Pointer for Arc<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Pointer::fmt(&*self._ptr, f)
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Default + Sync + Send> Default for Arc<T> {
     #[stable(feature = "rust1", since = "1.0.0")]

src/liballoc/boxed.rs

@@ -275,6 +275,16 @@ impl<T: fmt::Debug + ?Sized> fmt::Debug for Box<T> {
     }
 }
 
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> fmt::Pointer for Box<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // It's not possible to extract the inner Uniq directly from the Box,
+        // instead we cast it to a *const which aliases the Unique
+        let ptr: *const T = &**self;
+        fmt::Pointer::fmt(&ptr, f)
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized> Deref for Box<T> {
     type Target = T;

src/liballoc/rc.rs

@@ -634,6 +634,13 @@ impl<T: fmt::Debug> fmt::Debug for Rc<T> {
     }
 }
 
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> fmt::Pointer for Rc<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Pointer::fmt(&*self._ptr, f)
+    }
+}
+
 /// A weak version of `Rc<T>`.
 ///
 /// Weak references do not count when determining if the inner value should be

src/libcore/ptr.rs

@@ -94,6 +94,7 @@ use mem;
 use clone::Clone;
 use intrinsics;
 use ops::Deref;
+use core::fmt;
 use option::Option::{self, Some, None};
 use marker::{PhantomData, Send, Sized, Sync};
 use nonzero::NonZero;
@@ -570,3 +571,10 @@ impl<T:?Sized> Deref for Unique<T> {
         unsafe { mem::transmute(&*self.pointer) }
     }
 }
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> fmt::Pointer for Unique<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Pointer::fmt(&*self.pointer, f)
+    }
+}

src/libsyntax/ptr.rs

@@ -111,6 +111,13 @@ impl<T: Display> Display for P<T> {
     }
 }
 
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> fmt::Pointer for P<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Pointer::fmt(&self.ptr, f)
+    }
+}
+
 impl<T: Hash> Hash for P<T> {
     fn hash<H: Hasher>(&self, state: &mut H) {
         (**self).hash(state);

src/test/run-pass/fmt-pointer-trait.rs

@@ -0,0 +1,28 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(libc)]
+extern crate libc;
+use std::ptr;
+use std::rc::Rc;
+use std::sync::Arc;
+
+fn main() {
+    let p: *const libc::c_void = ptr::null();
+    let rc = Rc::new(1usize);
+    let arc = Arc::new(1usize);
+    let b = Box::new("hi");
+
+    let _ = format!("{:p}{:p}{:p}",
+                    rc, arc, b);
+
+    assert_eq!(format!("{:p}", p),
+               "0x0");
+}