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, uninit};
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 #[stable(feature = "rust1", since = "1.0.0")]
195 impl<T: ?Sized> !marker::Send for Rc<T> {}
196 #[stable(feature = "rust1", since = "1.0.0")]
197 impl<T: ?Sized> !marker::Sync for Rc<T> {}
199 // remove cfg after new snapshot
201 #[unstable(feature = "coerce_unsized", issue = "27732")]
202 impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Rc<U>> for Rc<T> {}
205 /// Constructs a new `Rc<T>`.
212 /// let five = Rc::new(5);
214 #[stable(feature = "rust1", since = "1.0.0")]
215 pub fn new(value: T) -> Rc<T> {
218 // there is an implicit weak pointer owned by all the strong
219 // pointers, which ensures that the weak destructor never frees
220 // the allocation while the strong destructor is running, even
221 // if the weak pointer is stored inside the strong one.
222 _ptr: Shared::new(Box::into_raw(box RcBox {
223 strong: Cell::new(1),
231 /// Unwraps the contained value if the `Rc<T>` has only one strong reference.
232 /// This will succeed even if there are outstanding weak references.
234 /// Otherwise, an `Err` is returned with the same `Rc<T>`.
241 /// let x = Rc::new(3);
242 /// assert_eq!(Rc::try_unwrap(x), Ok(3));
244 /// let x = Rc::new(4);
245 /// let _y = x.clone();
246 /// assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4)));
249 #[stable(feature = "rc_unique", since = "1.4.0")]
250 pub fn try_unwrap(this: Self) -> Result<T, Self> {
251 if Rc::would_unwrap(&this) {
253 let val = ptr::read(&*this); // copy the contained object
255 // Indicate to Weaks that they can't be promoted by decrememting
256 // the strong count, and then remove the implicit "strong weak"
257 // pointer while also handling drop logic by just crafting a
260 let _weak = Weak { _ptr: this._ptr };
269 /// Checks if `Rc::try_unwrap` would return `Ok`.
270 #[unstable(feature = "rc_would_unwrap",
271 reason = "just added for niche usecase",
273 pub fn would_unwrap(this: &Self) -> bool {
274 Rc::strong_count(&this) == 1
278 impl<T: ?Sized> Rc<T> {
279 /// Downgrades the `Rc<T>` to a `Weak<T>` reference.
286 /// let five = Rc::new(5);
288 /// let weak_five = Rc::downgrade(&five);
290 #[stable(feature = "rc_weak", since = "1.4.0")]
291 pub fn downgrade(this: &Self) -> Weak<T> {
293 Weak { _ptr: this._ptr }
296 /// Get the number of weak references to this value.
298 #[unstable(feature = "rc_counts", reason = "not clearly useful",
300 pub fn weak_count(this: &Self) -> usize {
304 /// Get the number of strong references to this value.
306 #[unstable(feature = "rc_counts", reason = "not clearly useful",
308 pub fn strong_count(this: &Self) -> usize {
312 /// Returns true if there are no other `Rc` or `Weak<T>` values that share
313 /// the same inner value.
318 /// #![feature(rc_counts)]
322 /// let five = Rc::new(5);
324 /// assert!(Rc::is_unique(&five));
327 #[unstable(feature = "rc_counts", reason = "uniqueness has unclear meaning",
329 pub fn is_unique(this: &Self) -> bool {
330 Rc::weak_count(this) == 0 && Rc::strong_count(this) == 1
333 /// Returns a mutable reference to the contained value if the `Rc<T>` has
334 /// one strong reference and no weak references.
336 /// Returns `None` if the `Rc<T>` is not unique.
343 /// let mut x = Rc::new(3);
344 /// *Rc::get_mut(&mut x).unwrap() = 4;
345 /// assert_eq!(*x, 4);
347 /// let _y = x.clone();
348 /// assert!(Rc::get_mut(&mut x).is_none());
351 #[stable(feature = "rc_unique", since = "1.4.0")]
352 pub fn get_mut(this: &mut Self) -> Option<&mut T> {
353 if Rc::is_unique(this) {
354 let inner = unsafe { &mut **this._ptr };
355 Some(&mut inner.value)
362 impl<T: Clone> Rc<T> {
363 /// Make a mutable reference into the given `Rc<T>` by cloning the inner
364 /// data if the `Rc<T>` doesn't have one strong reference and no weak
367 /// This is also referred to as a copy-on-write.
374 /// let mut data = Rc::new(5);
376 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
377 /// let mut other_data = data.clone(); // Won't clone inner data
378 /// *Rc::make_mut(&mut data) += 1; // Clones inner data
379 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
380 /// *Rc::make_mut(&mut other_data) *= 2; // Won't clone anything
382 /// // Note: data and other_data now point to different numbers
383 /// assert_eq!(*data, 8);
384 /// assert_eq!(*other_data, 12);
388 #[stable(feature = "rc_unique", since = "1.4.0")]
389 pub fn make_mut(this: &mut Self) -> &mut T {
390 if Rc::strong_count(this) != 1 {
391 // Gotta clone the data, there are other Rcs
392 *this = Rc::new((**this).clone())
393 } else if Rc::weak_count(this) != 0 {
394 // Can just steal the data, all that's left is Weaks
396 let mut swap = Rc::new(ptr::read(&(**this._ptr).value));
397 mem::swap(this, &mut swap);
399 // Remove implicit strong-weak ref (no need to craft a fake
400 // Weak here -- we know other Weaks can clean up for us)
405 // This unsafety is ok because we're guaranteed that the pointer
406 // returned is the *only* pointer that will ever be returned to T. Our
407 // reference count is guaranteed to be 1 at this point, and we required
408 // the `Rc<T>` itself to be `mut`, so we're returning the only possible
409 // reference to the inner value.
410 let inner = unsafe { &mut **this._ptr };
415 #[stable(feature = "rust1", since = "1.0.0")]
416 impl<T: ?Sized> Deref for Rc<T> {
420 fn deref(&self) -> &T {
425 #[stable(feature = "rust1", since = "1.0.0")]
426 impl<T: ?Sized> Drop for Rc<T> {
427 /// Drops the `Rc<T>`.
429 /// This will decrement the strong reference count. If the strong reference
430 /// count becomes zero and the only other references are `Weak<T>` ones,
431 /// `drop`s the inner value.
439 /// let five = Rc::new(5);
443 /// drop(five); // explicit drop
446 /// let five = Rc::new(5);
450 /// } // implicit drop
452 #[unsafe_destructor_blind_to_params]
455 let ptr = *self._ptr;
456 if !(*(&ptr as *const _ as *const *const ())).is_null() &&
457 ptr as *const () as usize != mem::POST_DROP_USIZE {
459 if self.strong() == 0 {
460 // destroy the contained object
461 ptr::drop_in_place(&mut (*ptr).value);
463 // remove the implicit "strong weak" pointer now that we've
464 // destroyed the contents.
467 if self.weak() == 0 {
468 deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
476 #[stable(feature = "rust1", since = "1.0.0")]
477 impl<T: ?Sized> Clone for Rc<T> {
478 /// Makes a clone of the `Rc<T>`.
480 /// When you clone an `Rc<T>`, it will create another pointer to the data and
481 /// increase the strong reference counter.
488 /// let five = Rc::new(5);
493 fn clone(&self) -> Rc<T> {
495 Rc { _ptr: self._ptr }
499 #[stable(feature = "rust1", since = "1.0.0")]
500 impl<T: Default> Default for Rc<T> {
501 /// Creates a new `Rc<T>`, with the `Default` value for `T`.
508 /// let x: Rc<i32> = Default::default();
511 fn default() -> Rc<T> {
512 Rc::new(Default::default())
516 #[stable(feature = "rust1", since = "1.0.0")]
517 impl<T: ?Sized + PartialEq> PartialEq for Rc<T> {
518 /// Equality for two `Rc<T>`s.
520 /// Two `Rc<T>`s are equal if their inner value are equal.
527 /// let five = Rc::new(5);
529 /// five == Rc::new(5);
532 fn eq(&self, other: &Rc<T>) -> bool {
536 /// Inequality for two `Rc<T>`s.
538 /// Two `Rc<T>`s are unequal if their inner value are unequal.
545 /// let five = Rc::new(5);
547 /// five != Rc::new(5);
550 fn ne(&self, other: &Rc<T>) -> bool {
555 #[stable(feature = "rust1", since = "1.0.0")]
556 impl<T: ?Sized + Eq> Eq for Rc<T> {}
558 #[stable(feature = "rust1", since = "1.0.0")]
559 impl<T: ?Sized + PartialOrd> PartialOrd for Rc<T> {
560 /// Partial comparison for two `Rc<T>`s.
562 /// The two are compared by calling `partial_cmp()` on their inner values.
569 /// let five = Rc::new(5);
571 /// five.partial_cmp(&Rc::new(5));
574 fn partial_cmp(&self, other: &Rc<T>) -> Option<Ordering> {
575 (**self).partial_cmp(&**other)
578 /// Less-than comparison for two `Rc<T>`s.
580 /// The two are compared by calling `<` on their inner values.
587 /// let five = Rc::new(5);
589 /// five < Rc::new(5);
592 fn lt(&self, other: &Rc<T>) -> bool {
596 /// 'Less-than or equal to' comparison for two `Rc<T>`s.
598 /// The two are compared by calling `<=` on their inner values.
605 /// let five = Rc::new(5);
607 /// five <= Rc::new(5);
610 fn le(&self, other: &Rc<T>) -> bool {
614 /// Greater-than comparison for two `Rc<T>`s.
616 /// The two are compared by calling `>` on their inner values.
623 /// let five = Rc::new(5);
625 /// five > Rc::new(5);
628 fn gt(&self, other: &Rc<T>) -> bool {
632 /// 'Greater-than or equal to' comparison for two `Rc<T>`s.
634 /// The two are compared by calling `>=` on their inner values.
641 /// let five = Rc::new(5);
643 /// five >= Rc::new(5);
646 fn ge(&self, other: &Rc<T>) -> bool {
651 #[stable(feature = "rust1", since = "1.0.0")]
652 impl<T: ?Sized + Ord> Ord for Rc<T> {
653 /// Comparison for two `Rc<T>`s.
655 /// The two are compared by calling `cmp()` on their inner values.
662 /// let five = Rc::new(5);
664 /// five.partial_cmp(&Rc::new(5));
667 fn cmp(&self, other: &Rc<T>) -> Ordering {
668 (**self).cmp(&**other)
672 #[stable(feature = "rust1", since = "1.0.0")]
673 impl<T: ?Sized + Hash> Hash for Rc<T> {
674 fn hash<H: Hasher>(&self, state: &mut H) {
675 (**self).hash(state);
679 #[stable(feature = "rust1", since = "1.0.0")]
680 impl<T: ?Sized + fmt::Display> fmt::Display for Rc<T> {
681 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
682 fmt::Display::fmt(&**self, f)
686 #[stable(feature = "rust1", since = "1.0.0")]
687 impl<T: ?Sized + fmt::Debug> fmt::Debug for Rc<T> {
688 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
689 fmt::Debug::fmt(&**self, f)
693 #[stable(feature = "rust1", since = "1.0.0")]
694 impl<T> fmt::Pointer for Rc<T> {
695 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
696 fmt::Pointer::fmt(&*self._ptr, f)
700 #[stable(feature = "from_for_ptrs", since = "1.6.0")]
701 impl<T> From<T> for Rc<T> {
702 fn from(t: T) -> Self {
707 /// A weak version of `Rc<T>`.
709 /// Weak references do not count when determining if the inner value should be
712 /// See the [module level documentation](./index.html) for more.
713 #[unsafe_no_drop_flag]
714 #[stable(feature = "rc_weak", since = "1.4.0")]
715 pub struct Weak<T: ?Sized> {
716 // FIXME #12808: strange names to try to avoid interfering with
717 // field accesses of the contained type via Deref
718 _ptr: Shared<RcBox<T>>,
721 #[stable(feature = "rust1", since = "1.0.0")]
722 impl<T: ?Sized> !marker::Send for Weak<T> {}
723 #[stable(feature = "rust1", since = "1.0.0")]
724 impl<T: ?Sized> !marker::Sync for Weak<T> {}
726 // remove cfg after new snapshot
728 #[unstable(feature = "coerce_unsized", issue = "27732")]
729 impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {}
731 impl<T: ?Sized> Weak<T> {
732 /// Upgrades a weak reference to a strong reference.
734 /// Upgrades the `Weak<T>` reference to an `Rc<T>`, if possible.
736 /// Returns `None` if there were no strong references and the data was
744 /// let five = Rc::new(5);
746 /// let weak_five = Rc::downgrade(&five);
748 /// let strong_five: Option<Rc<_>> = weak_five.upgrade();
750 #[stable(feature = "rc_weak", since = "1.4.0")]
751 pub fn upgrade(&self) -> Option<Rc<T>> {
752 if self.strong() == 0 {
756 Some(Rc { _ptr: self._ptr })
761 #[stable(feature = "rust1", since = "1.0.0")]
762 impl<T: ?Sized> Drop for Weak<T> {
763 /// Drops the `Weak<T>`.
765 /// This will decrement the weak reference count.
773 /// let five = Rc::new(5);
774 /// let weak_five = Rc::downgrade(&five);
778 /// drop(weak_five); // explicit drop
781 /// let five = Rc::new(5);
782 /// let weak_five = Rc::downgrade(&five);
786 /// } // implicit drop
790 let ptr = *self._ptr;
791 if !(*(&ptr as *const _ as *const *const ())).is_null() &&
792 ptr as *const () as usize != mem::POST_DROP_USIZE {
794 // the weak count starts at 1, and will only go to zero if all
795 // the strong pointers have disappeared.
796 if self.weak() == 0 {
797 deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
804 #[stable(feature = "rc_weak", since = "1.4.0")]
805 impl<T: ?Sized> Clone for Weak<T> {
806 /// Makes a clone of the `Weak<T>`.
808 /// This increases the weak reference count.
815 /// let weak_five = Rc::downgrade(&Rc::new(5));
817 /// weak_five.clone();
820 fn clone(&self) -> Weak<T> {
822 Weak { _ptr: self._ptr }
826 #[stable(feature = "rust1", since = "1.0.0")]
827 impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> {
828 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
834 /// Constructs a new `Weak<T>` without an accompanying instance of T.
836 /// This allocates memory for T, but does not initialize it. Calling
837 /// Weak<T>::upgrade() on the return value always gives None.
842 /// use std::rc::Weak;
844 /// let five = Weak::new_downgraded();
847 #[unstable(feature = "downgraded_weak",
848 reason = "recently added",
850 pub fn new_downgraded() -> Weak<T> {
853 _ptr: Shared::new(Box::into_raw(box RcBox {
854 strong: Cell::new(0),
863 // NOTE: We checked_add here to deal with mem::forget safety. In particular
864 // if you mem::forget Rcs (or Weaks), the ref-count can overflow, and then
865 // you can free the allocation while outstanding Rcs (or Weaks) exist.
866 // We abort because this is such a degenerate scenario that we don't care about
867 // what happens -- no real program should ever experience this.
869 // This should have negligible overhead since you don't actually need to
870 // clone these much in Rust thanks to ownership and move-semantics.
873 trait RcBoxPtr<T: ?Sized> {
874 fn inner(&self) -> &RcBox<T>;
877 fn strong(&self) -> usize {
878 self.inner().strong.get()
882 fn inc_strong(&self) {
883 self.inner().strong.set(self.strong().checked_add(1).unwrap_or_else(|| unsafe { abort() }));
887 fn dec_strong(&self) {
888 self.inner().strong.set(self.strong() - 1);
892 fn weak(&self) -> usize {
893 self.inner().weak.get()
898 self.inner().weak.set(self.weak().checked_add(1).unwrap_or_else(|| unsafe { abort() }));
903 self.inner().weak.set(self.weak() - 1);
907 impl<T: ?Sized> RcBoxPtr<T> for Rc<T> {
909 fn inner(&self) -> &RcBox<T> {
911 // Safe to assume this here, as if it weren't true, we'd be breaking
912 // the contract anyway.
913 // This allows the null check to be elided in the destructor if we
914 // manipulated the reference count in the same function.
915 assume(!(*(&self._ptr as *const _ as *const *const ())).is_null());
921 impl<T: ?Sized> RcBoxPtr<T> for Weak<T> {
923 fn inner(&self) -> &RcBox<T> {
925 // Safe to assume this here, as if it weren't true, we'd be breaking
926 // the contract anyway.
927 // This allows the null check to be elided in the destructor if we
928 // manipulated the reference count in the same function.
929 assume(!(*(&self._ptr as *const _ as *const *const ())).is_null());
937 use super::{Rc, Weak};
939 use std::cell::RefCell;
940 use std::option::Option;
941 use std::option::Option::{Some, None};
942 use std::result::Result::{Err, Ok};
944 use std::clone::Clone;
945 use std::convert::From;
949 let x = Rc::new(RefCell::new(5));
951 *x.borrow_mut() = 20;
952 assert_eq!(*y.borrow(), 20);
962 fn test_simple_clone() {
970 fn test_destructor() {
971 let x: Rc<Box<_>> = Rc::new(box 5);
978 let y = Rc::downgrade(&x);
979 assert!(y.upgrade().is_some());
985 let y = Rc::downgrade(&x);
987 assert!(y.upgrade().is_none());
991 fn weak_self_cyclic() {
993 x: RefCell<Option<Weak<Cycle>>>,
996 let a = Rc::new(Cycle { x: RefCell::new(None) });
997 let b = Rc::downgrade(&a.clone());
998 *a.x.borrow_mut() = Some(b);
1000 // hopefully we don't double-free (or leak)...
1006 assert!(Rc::is_unique(&x));
1008 assert!(!Rc::is_unique(&x));
1010 assert!(Rc::is_unique(&x));
1011 let w = Rc::downgrade(&x);
1012 assert!(!Rc::is_unique(&x));
1014 assert!(Rc::is_unique(&x));
1018 fn test_strong_count() {
1019 let a = Rc::new(0u32);
1020 assert!(Rc::strong_count(&a) == 1);
1021 let w = Rc::downgrade(&a);
1022 assert!(Rc::strong_count(&a) == 1);
1023 let b = w.upgrade().expect("upgrade of live rc failed");
1024 assert!(Rc::strong_count(&b) == 2);
1025 assert!(Rc::strong_count(&a) == 2);
1028 assert!(Rc::strong_count(&b) == 1);
1030 assert!(Rc::strong_count(&b) == 2);
1031 assert!(Rc::strong_count(&c) == 2);
1035 fn test_weak_count() {
1036 let a = Rc::new(0u32);
1037 assert!(Rc::strong_count(&a) == 1);
1038 assert!(Rc::weak_count(&a) == 0);
1039 let w = Rc::downgrade(&a);
1040 assert!(Rc::strong_count(&a) == 1);
1041 assert!(Rc::weak_count(&a) == 1);
1043 assert!(Rc::strong_count(&a) == 1);
1044 assert!(Rc::weak_count(&a) == 0);
1046 assert!(Rc::strong_count(&a) == 2);
1047 assert!(Rc::weak_count(&a) == 0);
1054 assert_eq!(Rc::try_unwrap(x), Ok(3));
1057 assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4)));
1059 let _w = Rc::downgrade(&x);
1060 assert_eq!(Rc::try_unwrap(x), Ok(5));
1065 let mut x = Rc::new(3);
1066 *Rc::get_mut(&mut x).unwrap() = 4;
1069 assert!(Rc::get_mut(&mut x).is_none());
1071 assert!(Rc::get_mut(&mut x).is_some());
1072 let _w = Rc::downgrade(&x);
1073 assert!(Rc::get_mut(&mut x).is_none());
1077 fn test_cowrc_clone_make_unique() {
1078 let mut cow0 = Rc::new(75);
1079 let mut cow1 = cow0.clone();
1080 let mut cow2 = cow1.clone();
1082 assert!(75 == *Rc::make_mut(&mut cow0));
1083 assert!(75 == *Rc::make_mut(&mut cow1));
1084 assert!(75 == *Rc::make_mut(&mut cow2));
1086 *Rc::make_mut(&mut cow0) += 1;
1087 *Rc::make_mut(&mut cow1) += 2;
1088 *Rc::make_mut(&mut cow2) += 3;
1090 assert!(76 == *cow0);
1091 assert!(77 == *cow1);
1092 assert!(78 == *cow2);
1094 // none should point to the same backing memory
1095 assert!(*cow0 != *cow1);
1096 assert!(*cow0 != *cow2);
1097 assert!(*cow1 != *cow2);
1101 fn test_cowrc_clone_unique2() {
1102 let mut cow0 = Rc::new(75);
1103 let cow1 = cow0.clone();
1104 let cow2 = cow1.clone();
1106 assert!(75 == *cow0);
1107 assert!(75 == *cow1);
1108 assert!(75 == *cow2);
1110 *Rc::make_mut(&mut cow0) += 1;
1112 assert!(76 == *cow0);
1113 assert!(75 == *cow1);
1114 assert!(75 == *cow2);
1116 // cow1 and cow2 should share the same contents
1117 // cow0 should have a unique reference
1118 assert!(*cow0 != *cow1);
1119 assert!(*cow0 != *cow2);
1120 assert!(*cow1 == *cow2);
1124 fn test_cowrc_clone_weak() {
1125 let mut cow0 = Rc::new(75);
1126 let cow1_weak = Rc::downgrade(&cow0);
1128 assert!(75 == *cow0);
1129 assert!(75 == *cow1_weak.upgrade().unwrap());
1131 *Rc::make_mut(&mut cow0) += 1;
1133 assert!(76 == *cow0);
1134 assert!(cow1_weak.upgrade().is_none());
1139 let foo = Rc::new(75);
1140 assert_eq!(format!("{:?}", foo), "75");
1145 let foo: Rc<[i32]> = Rc::new([1, 2, 3]);
1146 assert_eq!(foo, foo.clone());
1150 fn test_from_owned() {
1152 let foo_rc = Rc::from(foo);
1153 assert!(123 == *foo_rc);
1157 fn test_new_downgraded() {
1158 let foo: Weak<usize> = Weak::new_downgraded();
1159 assert!(foo.upgrade().is_none());
1163 #[stable(feature = "rust1", since = "1.0.0")]
1164 impl<T: ?Sized> borrow::Borrow<T> for Rc<T> {
1165 fn borrow(&self) -> &T {
1170 #[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
1171 impl<T: ?Sized> AsRef<T> for Rc<T> {
1172 fn as_ref(&self) -> &T {