1 // Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
13 //! Thread-local reference-counted boxes (the `Rc<T>` type).
15 //! The `Rc<T>` type provides shared ownership of an immutable value.
16 //! Destruction is deterministic, and will occur as soon as the last owner is
17 //! gone. It is marked as non-sendable because it avoids the overhead of atomic
18 //! reference counting.
20 //! The `downgrade` method can be used to create a non-owning `Weak<T>` pointer
21 //! to the box. A `Weak<T>` pointer can be upgraded to an `Rc<T>` pointer, but
22 //! will return `None` if the value has already been dropped.
24 //! For example, a tree with parent pointers can be represented by putting the
25 //! nodes behind strong `Rc<T>` pointers, and then storing the parent pointers
26 //! as `Weak<T>` pointers.
30 //! Consider a scenario where a set of `Gadget`s are owned by a given `Owner`.
31 //! We want to have our `Gadget`s point to their `Owner`. We can't do this with
32 //! unique ownership, because more than one gadget may belong to the same
33 //! `Owner`. `Rc<T>` allows us to share an `Owner` between multiple `Gadget`s,
34 //! and have the `Owner` remain allocated as long as any `Gadget` points at it.
41 //! // ...other fields
47 //! // ...other fields
51 //! // Create a reference counted Owner.
52 //! let gadget_owner : Rc<Owner> = Rc::new(
53 //! Owner { name: String::from("Gadget Man") }
56 //! // Create Gadgets belonging to gadget_owner. To increment the reference
57 //! // count we clone the `Rc<T>` object.
58 //! let gadget1 = Gadget { id: 1, owner: gadget_owner.clone() };
59 //! let gadget2 = Gadget { id: 2, owner: gadget_owner.clone() };
61 //! drop(gadget_owner);
63 //! // Despite dropping gadget_owner, we're still able to print out the name
64 //! // of the Owner of the Gadgets. This is because we've only dropped the
65 //! // reference count object, not the Owner it wraps. As long as there are
66 //! // other `Rc<T>` objects pointing at the same Owner, it will remain
67 //! // allocated. Notice that the `Rc<T>` wrapper around Gadget.owner gets
68 //! // automatically dereferenced for us.
69 //! println!("Gadget {} owned by {}", gadget1.id, gadget1.owner.name);
70 //! println!("Gadget {} owned by {}", gadget2.id, gadget2.owner.name);
72 //! // At the end of the method, gadget1 and gadget2 get destroyed, and with
73 //! // them the last counted references to our Owner. Gadget Man now gets
74 //! // destroyed as well.
78 //! If our requirements change, and we also need to be able to traverse from
79 //! Owner → Gadget, we will run into problems: an `Rc<T>` pointer from Owner
80 //! → Gadget introduces a cycle between the objects. This means that their
81 //! reference counts can never reach 0, and the objects will remain allocated: a
82 //! memory leak. In order to get around this, we can use `Weak<T>` pointers.
83 //! These pointers don't contribute to the total count.
85 //! Rust actually makes it somewhat difficult to produce this loop in the first
86 //! place: in order to end up with two objects that point at each other, one of
87 //! them needs to be mutable. This is problematic because `Rc<T>` enforces
88 //! memory safety by only giving out shared references to the object it wraps,
89 //! and these don't allow direct mutation. We need to wrap the part of the
90 //! object we wish to mutate in a `RefCell`, which provides *interior
91 //! mutability*: a method to achieve mutability through a shared reference.
92 //! `RefCell` enforces Rust's borrowing rules at runtime. Read the `Cell`
93 //! documentation for more details on interior mutability.
97 //! use std::rc::Weak;
98 //! use std::cell::RefCell;
102 //! gadgets: RefCell<Vec<Weak<Gadget>>>,
103 //! // ...other fields
108 //! owner: Rc<Owner>,
109 //! // ...other fields
113 //! // Create a reference counted Owner. Note the fact that we've put the
114 //! // Owner's vector of Gadgets inside a RefCell so that we can mutate it
115 //! // through a shared reference.
116 //! let gadget_owner : Rc<Owner> = Rc::new(
118 //! name: "Gadget Man".to_string(),
119 //! gadgets: RefCell::new(Vec::new()),
123 //! // Create Gadgets belonging to gadget_owner as before.
124 //! let gadget1 = Rc::new(Gadget{id: 1, owner: gadget_owner.clone()});
125 //! let gadget2 = Rc::new(Gadget{id: 2, owner: gadget_owner.clone()});
127 //! // Add the Gadgets to their Owner. To do this we mutably borrow from
128 //! // the RefCell holding the Owner's Gadgets.
129 //! gadget_owner.gadgets.borrow_mut().push(Rc::downgrade(&gadget1));
130 //! gadget_owner.gadgets.borrow_mut().push(Rc::downgrade(&gadget2));
132 //! // Iterate over our Gadgets, printing their details out
133 //! for gadget_opt in gadget_owner.gadgets.borrow().iter() {
135 //! // gadget_opt is a Weak<Gadget>. Since weak pointers can't guarantee
136 //! // that their object is still allocated, we need to call upgrade()
137 //! // on them to turn them into a strong reference. This returns an
138 //! // Option, which contains a reference to our object if it still
140 //! let gadget = gadget_opt.upgrade().unwrap();
141 //! println!("Gadget {} owned by {}", gadget.id, gadget.owner.name);
144 //! // At the end of the method, gadget_owner, gadget1 and gadget2 get
145 //! // destroyed. There are now no strong (`Rc<T>`) references to the gadgets.
146 //! // Once they get destroyed, the Gadgets get destroyed. This zeroes the
147 //! // reference count on Gadget Man, they get destroyed as well.
151 #![stable(feature = "rust1", since = "1.0.0")]
159 use core::cell::Cell;
160 use core::cmp::Ordering;
162 use core::hash::{Hasher, Hash};
163 use core::intrinsics::{assume, abort};
166 use core::marker::Unsize;
167 use core::mem::{self, align_of_val, size_of_val, forget};
168 use core::ops::Deref;
170 use core::ops::CoerceUnsized;
171 use core::ptr::{self, Shared};
172 use core::convert::From;
174 use heap::deallocate;
176 struct RcBox<T: ?Sized> {
183 /// A reference-counted pointer type over an immutable value.
185 /// See the [module level documentation](./index.html) for more details.
186 #[unsafe_no_drop_flag]
187 #[stable(feature = "rust1", since = "1.0.0")]
188 pub struct Rc<T: ?Sized> {
189 // FIXME #12808: strange names to try to avoid interfering with field
190 // accesses of the contained type via Deref
191 _ptr: Shared<RcBox<T>>,
194 impl<T: ?Sized> !marker::Send for Rc<T> {}
195 impl<T: ?Sized> !marker::Sync for Rc<T> {}
197 #[cfg(not(stage0))] // remove cfg after new snapshot
198 impl<T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<Rc<U>> for Rc<T> {}
201 /// Constructs a new `Rc<T>`.
208 /// let five = Rc::new(5);
210 #[stable(feature = "rust1", since = "1.0.0")]
211 pub fn new(value: T) -> Rc<T> {
214 // there is an implicit weak pointer owned by all the strong
215 // pointers, which ensures that the weak destructor never frees
216 // the allocation while the strong destructor is running, even
217 // if the weak pointer is stored inside the strong one.
218 _ptr: Shared::new(Box::into_raw(box RcBox {
219 strong: Cell::new(1),
227 /// Unwraps the contained value if the `Rc<T>` has only one strong reference.
228 /// This will succeed even if there are outstanding weak references.
230 /// Otherwise, an `Err` is returned with the same `Rc<T>`.
237 /// let x = Rc::new(3);
238 /// assert_eq!(Rc::try_unwrap(x), Ok(3));
240 /// let x = Rc::new(4);
241 /// let _y = x.clone();
242 /// assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4)));
245 #[stable(feature = "rc_unique", since = "1.4.0")]
246 pub fn try_unwrap(this: Self) -> Result<T, Self> {
247 if Rc::would_unwrap(&this) {
249 let val = ptr::read(&*this); // copy the contained object
251 // Indicate to Weaks that they can't be promoted by decrememting
252 // the strong count, and then remove the implicit "strong weak"
253 // pointer while also handling drop logic by just crafting a
256 let _weak = Weak { _ptr: this._ptr };
265 /// Checks if `Rc::try_unwrap` would return `Ok`.
266 #[unstable(feature = "rc_would_unwrap",
267 reason = "just added for niche usecase",
269 pub fn would_unwrap(this: &Self) -> bool {
270 Rc::strong_count(&this) == 1
274 impl<T: ?Sized> Rc<T> {
275 /// Downgrades the `Rc<T>` to a `Weak<T>` reference.
282 /// let five = Rc::new(5);
284 /// let weak_five = Rc::downgrade(&five);
286 #[stable(feature = "rc_weak", since = "1.4.0")]
287 pub fn downgrade(this: &Self) -> Weak<T> {
289 Weak { _ptr: this._ptr }
292 /// Get the number of weak references to this value.
294 #[unstable(feature = "rc_counts", reason = "not clearly useful",
296 pub fn weak_count(this: &Self) -> usize {
300 /// Get the number of strong references to this value.
302 #[unstable(feature = "rc_counts", reason = "not clearly useful",
304 pub fn strong_count(this: &Self) -> usize {
308 /// Returns true if there are no other `Rc` or `Weak<T>` values that share
309 /// the same inner value.
314 /// #![feature(rc_counts)]
318 /// let five = Rc::new(5);
320 /// assert!(Rc::is_unique(&five));
323 #[unstable(feature = "rc_counts", reason = "uniqueness has unclear meaning",
325 pub fn is_unique(this: &Self) -> bool {
326 Rc::weak_count(this) == 0 && Rc::strong_count(this) == 1
329 /// Returns a mutable reference to the contained value if the `Rc<T>` has
330 /// one strong reference and no weak references.
332 /// Returns `None` if the `Rc<T>` is not unique.
339 /// let mut x = Rc::new(3);
340 /// *Rc::get_mut(&mut x).unwrap() = 4;
341 /// assert_eq!(*x, 4);
343 /// let _y = x.clone();
344 /// assert!(Rc::get_mut(&mut x).is_none());
347 #[stable(feature = "rc_unique", since = "1.4.0")]
348 pub fn get_mut(this: &mut Self) -> Option<&mut T> {
349 if Rc::is_unique(this) {
350 let inner = unsafe { &mut **this._ptr };
351 Some(&mut inner.value)
358 impl<T: Clone> Rc<T> {
360 #[unstable(feature = "rc_make_unique", reason = "renamed to Rc::make_mut",
362 #[deprecated(since = "1.4.0", reason = "renamed to Rc::make_mut")]
363 pub fn make_unique(&mut self) -> &mut T {
367 /// Make a mutable reference into the given `Rc<T>` by cloning the inner
368 /// data if the `Rc<T>` doesn't have one strong reference and no weak
371 /// This is also referred to as a copy-on-write.
378 /// let mut data = Rc::new(5);
380 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
381 /// let mut other_data = data.clone(); // Won't clone inner data
382 /// *Rc::make_mut(&mut data) += 1; // Clones inner data
383 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
384 /// *Rc::make_mut(&mut other_data) *= 2; // Won't clone anything
386 /// // Note: data and other_data now point to different numbers
387 /// assert_eq!(*data, 8);
388 /// assert_eq!(*other_data, 12);
392 #[stable(feature = "rc_unique", since = "1.4.0")]
393 pub fn make_mut(this: &mut Self) -> &mut T {
394 if Rc::strong_count(this) != 1 {
395 // Gotta clone the data, there are other Rcs
396 *this = Rc::new((**this).clone())
397 } else if Rc::weak_count(this) != 0 {
398 // Can just steal the data, all that's left is Weaks
400 let mut swap = Rc::new(ptr::read(&(**this._ptr).value));
401 mem::swap(this, &mut swap);
403 // Remove implicit strong-weak ref (no need to craft a fake
404 // Weak here -- we know other Weaks can clean up for us)
409 // This unsafety is ok because we're guaranteed that the pointer
410 // returned is the *only* pointer that will ever be returned to T. Our
411 // reference count is guaranteed to be 1 at this point, and we required
412 // the `Rc<T>` itself to be `mut`, so we're returning the only possible
413 // reference to the inner value.
414 let inner = unsafe { &mut **this._ptr };
419 #[stable(feature = "rust1", since = "1.0.0")]
420 impl<T: ?Sized> Deref for Rc<T> {
424 fn deref(&self) -> &T {
429 #[stable(feature = "rust1", since = "1.0.0")]
430 impl<T: ?Sized> Drop for Rc<T> {
431 /// Drops the `Rc<T>`.
433 /// This will decrement the strong reference count. If the strong reference
434 /// count becomes zero and the only other references are `Weak<T>` ones,
435 /// `drop`s the inner value.
443 /// let five = Rc::new(5);
447 /// drop(five); // explicit drop
450 /// let five = Rc::new(5);
454 /// } // implicit drop
456 #[unsafe_destructor_blind_to_params]
459 let ptr = *self._ptr;
460 if !(*(&ptr as *const _ as *const *const ())).is_null() &&
461 ptr as *const () as usize != mem::POST_DROP_USIZE {
463 if self.strong() == 0 {
464 // destroy the contained object
465 ptr::drop_in_place(&mut (*ptr).value);
467 // remove the implicit "strong weak" pointer now that we've
468 // destroyed the contents.
471 if self.weak() == 0 {
472 deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
480 #[stable(feature = "rust1", since = "1.0.0")]
481 impl<T: ?Sized> Clone for Rc<T> {
483 /// Makes a clone of the `Rc<T>`.
485 /// When you clone an `Rc<T>`, it will create another pointer to the data and
486 /// increase the strong reference counter.
493 /// let five = Rc::new(5);
498 fn clone(&self) -> Rc<T> {
500 Rc { _ptr: self._ptr }
504 #[stable(feature = "rust1", since = "1.0.0")]
505 impl<T: Default> Default for Rc<T> {
506 /// Creates a new `Rc<T>`, with the `Default` value for `T`.
513 /// let x: Rc<i32> = Default::default();
516 fn default() -> Rc<T> {
517 Rc::new(Default::default())
521 #[stable(feature = "rust1", since = "1.0.0")]
522 impl<T: ?Sized + PartialEq> PartialEq for Rc<T> {
523 /// Equality for two `Rc<T>`s.
525 /// Two `Rc<T>`s are equal if their inner value are equal.
532 /// let five = Rc::new(5);
534 /// five == Rc::new(5);
537 fn eq(&self, other: &Rc<T>) -> bool {
541 /// Inequality for two `Rc<T>`s.
543 /// Two `Rc<T>`s are unequal if their inner value are unequal.
550 /// let five = Rc::new(5);
552 /// five != Rc::new(5);
555 fn ne(&self, other: &Rc<T>) -> bool {
560 #[stable(feature = "rust1", since = "1.0.0")]
561 impl<T: ?Sized + Eq> Eq for Rc<T> {}
563 #[stable(feature = "rust1", since = "1.0.0")]
564 impl<T: ?Sized + PartialOrd> PartialOrd for Rc<T> {
565 /// Partial comparison for two `Rc<T>`s.
567 /// The two are compared by calling `partial_cmp()` on their inner values.
574 /// let five = Rc::new(5);
576 /// five.partial_cmp(&Rc::new(5));
579 fn partial_cmp(&self, other: &Rc<T>) -> Option<Ordering> {
580 (**self).partial_cmp(&**other)
583 /// Less-than comparison for two `Rc<T>`s.
585 /// The two are compared by calling `<` on their inner values.
592 /// let five = Rc::new(5);
594 /// five < Rc::new(5);
597 fn lt(&self, other: &Rc<T>) -> bool {
601 /// 'Less-than or equal to' comparison for two `Rc<T>`s.
603 /// The two are compared by calling `<=` on their inner values.
610 /// let five = Rc::new(5);
612 /// five <= Rc::new(5);
615 fn le(&self, other: &Rc<T>) -> bool {
619 /// Greater-than comparison for two `Rc<T>`s.
621 /// The two are compared by calling `>` on their inner values.
628 /// let five = Rc::new(5);
630 /// five > Rc::new(5);
633 fn gt(&self, other: &Rc<T>) -> bool {
637 /// 'Greater-than or equal to' comparison for two `Rc<T>`s.
639 /// The two are compared by calling `>=` on their inner values.
646 /// let five = Rc::new(5);
648 /// five >= Rc::new(5);
651 fn ge(&self, other: &Rc<T>) -> bool {
656 #[stable(feature = "rust1", since = "1.0.0")]
657 impl<T: ?Sized + Ord> Ord for Rc<T> {
658 /// Comparison for two `Rc<T>`s.
660 /// The two are compared by calling `cmp()` on their inner values.
667 /// let five = Rc::new(5);
669 /// five.partial_cmp(&Rc::new(5));
672 fn cmp(&self, other: &Rc<T>) -> Ordering {
673 (**self).cmp(&**other)
677 #[stable(feature = "rust1", since = "1.0.0")]
678 impl<T: ?Sized+Hash> Hash for Rc<T> {
679 fn hash<H: Hasher>(&self, state: &mut H) {
680 (**self).hash(state);
684 #[stable(feature = "rust1", since = "1.0.0")]
685 impl<T: ?Sized+fmt::Display> fmt::Display for Rc<T> {
686 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
687 fmt::Display::fmt(&**self, f)
691 #[stable(feature = "rust1", since = "1.0.0")]
692 impl<T: ?Sized+fmt::Debug> fmt::Debug for Rc<T> {
693 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
694 fmt::Debug::fmt(&**self, f)
698 #[stable(feature = "rust1", since = "1.0.0")]
699 impl<T> fmt::Pointer for Rc<T> {
700 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
701 fmt::Pointer::fmt(&*self._ptr, f)
705 #[stable(feature = "from_for_ptrs", since = "1.6.0")]
706 impl<T> From<T> for Rc<T> {
707 fn from(t: T) -> Self {
712 /// A weak version of `Rc<T>`.
714 /// Weak references do not count when determining if the inner value should be
717 /// See the [module level documentation](./index.html) for more.
718 #[unsafe_no_drop_flag]
719 #[stable(feature = "rc_weak", since = "1.4.0")]
720 pub struct Weak<T: ?Sized> {
721 // FIXME #12808: strange names to try to avoid interfering with
722 // field accesses of the contained type via Deref
723 _ptr: Shared<RcBox<T>>,
726 impl<T: ?Sized> !marker::Send for Weak<T> {}
727 impl<T: ?Sized> !marker::Sync for Weak<T> {}
729 #[cfg(not(stage0))] // remove cfg after new snapshot
730 impl<T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {}
732 impl<T: ?Sized> Weak<T> {
733 /// Upgrades a weak reference to a strong reference.
735 /// Upgrades the `Weak<T>` reference to an `Rc<T>`, if possible.
737 /// Returns `None` if there were no strong references and the data was
745 /// let five = Rc::new(5);
747 /// let weak_five = Rc::downgrade(&five);
749 /// let strong_five: Option<Rc<_>> = weak_five.upgrade();
751 #[stable(feature = "rc_weak", since = "1.4.0")]
752 pub fn upgrade(&self) -> Option<Rc<T>> {
753 if self.strong() == 0 {
757 Some(Rc { _ptr: self._ptr })
762 #[stable(feature = "rust1", since = "1.0.0")]
763 impl<T: ?Sized> Drop for Weak<T> {
764 /// Drops the `Weak<T>`.
766 /// This will decrement the weak reference count.
774 /// let five = Rc::new(5);
775 /// let weak_five = Rc::downgrade(&five);
779 /// drop(weak_five); // explicit drop
782 /// let five = Rc::new(5);
783 /// let weak_five = Rc::downgrade(&five);
787 /// } // implicit drop
791 let ptr = *self._ptr;
792 if !(*(&ptr as *const _ as *const *const ())).is_null() &&
793 ptr as *const () as usize != mem::POST_DROP_USIZE {
795 // the weak count starts at 1, and will only go to zero if all
796 // the strong pointers have disappeared.
797 if self.weak() == 0 {
798 deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
805 #[stable(feature = "rc_weak", since = "1.4.0")]
806 impl<T: ?Sized> Clone for Weak<T> {
808 /// Makes a clone of the `Weak<T>`.
810 /// This increases the weak reference count.
817 /// let weak_five = Rc::downgrade(&Rc::new(5));
819 /// weak_five.clone();
822 fn clone(&self) -> Weak<T> {
824 Weak { _ptr: self._ptr }
828 #[stable(feature = "rust1", since = "1.0.0")]
829 impl<T: ?Sized+fmt::Debug> fmt::Debug for Weak<T> {
830 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
835 // NOTE: We checked_add here to deal with mem::forget safety. In particular
836 // if you mem::forget Rcs (or Weaks), the ref-count can overflow, and then
837 // you can free the allocation while outstanding Rcs (or Weaks) exist.
838 // We abort because this is such a degenerate scenario that we don't care about
839 // what happens -- no real program should ever experience this.
841 // This should have negligible overhead since you don't actually need to
842 // clone these much in Rust thanks to ownership and move-semantics.
845 trait RcBoxPtr<T: ?Sized> {
846 fn inner(&self) -> &RcBox<T>;
849 fn strong(&self) -> usize {
850 self.inner().strong.get()
854 fn inc_strong(&self) {
855 self.inner().strong.set(self.strong().checked_add(1).unwrap_or_else(|| unsafe { abort() }));
859 fn dec_strong(&self) {
860 self.inner().strong.set(self.strong() - 1);
864 fn weak(&self) -> usize {
865 self.inner().weak.get()
870 self.inner().weak.set(self.weak().checked_add(1).unwrap_or_else(|| unsafe { abort() }));
875 self.inner().weak.set(self.weak() - 1);
879 impl<T: ?Sized> RcBoxPtr<T> for Rc<T> {
881 fn inner(&self) -> &RcBox<T> {
883 // Safe to assume this here, as if it weren't true, we'd be breaking
884 // the contract anyway.
885 // This allows the null check to be elided in the destructor if we
886 // manipulated the reference count in the same function.
887 assume(!(*(&self._ptr as *const _ as *const *const ())).is_null());
893 impl<T: ?Sized> RcBoxPtr<T> for Weak<T> {
895 fn inner(&self) -> &RcBox<T> {
897 // Safe to assume this here, as if it weren't true, we'd be breaking
898 // the contract anyway.
899 // This allows the null check to be elided in the destructor if we
900 // manipulated the reference count in the same function.
901 assume(!(*(&self._ptr as *const _ as *const *const ())).is_null());
909 use super::{Rc, Weak};
911 use std::cell::RefCell;
912 use std::option::Option;
913 use std::option::Option::{Some, None};
914 use std::result::Result::{Err, Ok};
916 use std::clone::Clone;
917 use std::convert::From;
921 let x = Rc::new(RefCell::new(5));
923 *x.borrow_mut() = 20;
924 assert_eq!(*y.borrow(), 20);
934 fn test_simple_clone() {
942 fn test_destructor() {
943 let x: Rc<Box<_>> = Rc::new(box 5);
950 let y = Rc::downgrade(&x);
951 assert!(y.upgrade().is_some());
957 let y = Rc::downgrade(&x);
959 assert!(y.upgrade().is_none());
963 fn weak_self_cyclic() {
965 x: RefCell<Option<Weak<Cycle>>>,
968 let a = Rc::new(Cycle { x: RefCell::new(None) });
969 let b = Rc::downgrade(&a.clone());
970 *a.x.borrow_mut() = Some(b);
972 // hopefully we don't double-free (or leak)...
978 assert!(Rc::is_unique(&x));
980 assert!(!Rc::is_unique(&x));
982 assert!(Rc::is_unique(&x));
983 let w = Rc::downgrade(&x);
984 assert!(!Rc::is_unique(&x));
986 assert!(Rc::is_unique(&x));
990 fn test_strong_count() {
991 let a = Rc::new(0u32);
992 assert!(Rc::strong_count(&a) == 1);
993 let w = Rc::downgrade(&a);
994 assert!(Rc::strong_count(&a) == 1);
995 let b = w.upgrade().expect("upgrade of live rc failed");
996 assert!(Rc::strong_count(&b) == 2);
997 assert!(Rc::strong_count(&a) == 2);
1000 assert!(Rc::strong_count(&b) == 1);
1002 assert!(Rc::strong_count(&b) == 2);
1003 assert!(Rc::strong_count(&c) == 2);
1007 fn test_weak_count() {
1008 let a = Rc::new(0u32);
1009 assert!(Rc::strong_count(&a) == 1);
1010 assert!(Rc::weak_count(&a) == 0);
1011 let w = Rc::downgrade(&a);
1012 assert!(Rc::strong_count(&a) == 1);
1013 assert!(Rc::weak_count(&a) == 1);
1015 assert!(Rc::strong_count(&a) == 1);
1016 assert!(Rc::weak_count(&a) == 0);
1018 assert!(Rc::strong_count(&a) == 2);
1019 assert!(Rc::weak_count(&a) == 0);
1026 assert_eq!(Rc::try_unwrap(x), Ok(3));
1029 assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4)));
1031 let _w = Rc::downgrade(&x);
1032 assert_eq!(Rc::try_unwrap(x), Ok(5));
1037 let mut x = Rc::new(3);
1038 *Rc::get_mut(&mut x).unwrap() = 4;
1041 assert!(Rc::get_mut(&mut x).is_none());
1043 assert!(Rc::get_mut(&mut x).is_some());
1044 let _w = Rc::downgrade(&x);
1045 assert!(Rc::get_mut(&mut x).is_none());
1049 fn test_cowrc_clone_make_unique() {
1050 let mut cow0 = Rc::new(75);
1051 let mut cow1 = cow0.clone();
1052 let mut cow2 = cow1.clone();
1054 assert!(75 == *Rc::make_mut(&mut cow0));
1055 assert!(75 == *Rc::make_mut(&mut cow1));
1056 assert!(75 == *Rc::make_mut(&mut cow2));
1058 *Rc::make_mut(&mut cow0) += 1;
1059 *Rc::make_mut(&mut cow1) += 2;
1060 *Rc::make_mut(&mut cow2) += 3;
1062 assert!(76 == *cow0);
1063 assert!(77 == *cow1);
1064 assert!(78 == *cow2);
1066 // none should point to the same backing memory
1067 assert!(*cow0 != *cow1);
1068 assert!(*cow0 != *cow2);
1069 assert!(*cow1 != *cow2);
1073 fn test_cowrc_clone_unique2() {
1074 let mut cow0 = Rc::new(75);
1075 let cow1 = cow0.clone();
1076 let cow2 = cow1.clone();
1078 assert!(75 == *cow0);
1079 assert!(75 == *cow1);
1080 assert!(75 == *cow2);
1082 *Rc::make_mut(&mut cow0) += 1;
1084 assert!(76 == *cow0);
1085 assert!(75 == *cow1);
1086 assert!(75 == *cow2);
1088 // cow1 and cow2 should share the same contents
1089 // cow0 should have a unique reference
1090 assert!(*cow0 != *cow1);
1091 assert!(*cow0 != *cow2);
1092 assert!(*cow1 == *cow2);
1096 fn test_cowrc_clone_weak() {
1097 let mut cow0 = Rc::new(75);
1098 let cow1_weak = Rc::downgrade(&cow0);
1100 assert!(75 == *cow0);
1101 assert!(75 == *cow1_weak.upgrade().unwrap());
1103 *Rc::make_mut(&mut cow0) += 1;
1105 assert!(76 == *cow0);
1106 assert!(cow1_weak.upgrade().is_none());
1111 let foo = Rc::new(75);
1112 assert_eq!(format!("{:?}", foo), "75");
1117 let foo: Rc<[i32]> = Rc::new([1, 2, 3]);
1118 assert_eq!(foo, foo.clone());
1122 fn test_from_owned() {
1124 let foo_rc = Rc::from(foo);
1125 assert!(123 == *foo_rc);
1129 impl<T: ?Sized> borrow::Borrow<T> for Rc<T> {
1130 fn borrow(&self) -> &T {
1135 #[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
1136 impl<T: ?Sized> AsRef<T> for Rc<T> {
1137 fn as_ref(&self) -> &T {