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};
165 use core::marker::Unsize;
166 use core::mem::{self, align_of_val, size_of_val, forget, uninitialized};
167 use core::ops::Deref;
168 use core::ops::CoerceUnsized;
169 use core::ptr::{self, Shared};
170 use core::convert::From;
172 use heap::deallocate;
174 struct RcBox<T: ?Sized> {
181 /// A reference-counted pointer type over an immutable value.
183 /// See the [module level documentation](./index.html) for more details.
184 #[unsafe_no_drop_flag]
185 #[stable(feature = "rust1", since = "1.0.0")]
186 pub struct Rc<T: ?Sized> {
187 ptr: Shared<RcBox<T>>,
190 #[stable(feature = "rust1", since = "1.0.0")]
191 impl<T: ?Sized> !marker::Send for Rc<T> {}
192 #[stable(feature = "rust1", since = "1.0.0")]
193 impl<T: ?Sized> !marker::Sync for Rc<T> {}
195 #[unstable(feature = "coerce_unsized", issue = "27732")]
196 impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Rc<U>> for Rc<T> {}
199 /// Constructs a new `Rc<T>`.
206 /// let five = Rc::new(5);
208 #[stable(feature = "rust1", since = "1.0.0")]
209 pub fn new(value: T) -> Rc<T> {
212 // there is an implicit weak pointer owned by all the strong
213 // pointers, which ensures that the weak destructor never frees
214 // the allocation while the strong destructor is running, even
215 // if the weak pointer is stored inside the strong one.
216 ptr: Shared::new(Box::into_raw(box RcBox {
217 strong: Cell::new(1),
225 /// Unwraps the contained value if the `Rc<T>` has exactly one strong reference.
227 /// Otherwise, an `Err` is returned with the same `Rc<T>`.
229 /// This will succeed even if there are outstanding weak references.
236 /// let x = Rc::new(3);
237 /// assert_eq!(Rc::try_unwrap(x), Ok(3));
239 /// let x = Rc::new(4);
240 /// let _y = x.clone();
241 /// assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4)));
244 #[stable(feature = "rc_unique", since = "1.4.0")]
245 pub fn try_unwrap(this: Self) -> Result<T, Self> {
246 if Rc::would_unwrap(&this) {
248 let val = ptr::read(&*this); // copy the contained object
250 // Indicate to Weaks that they can't be promoted by decrememting
251 // the strong count, and then remove the implicit "strong weak"
252 // pointer while also handling drop logic by just crafting a
255 let _weak = Weak { ptr: this.ptr };
264 /// Checks if `Rc::try_unwrap` would return `Ok`.
265 #[unstable(feature = "rc_would_unwrap",
266 reason = "just added for niche usecase",
268 pub fn would_unwrap(this: &Self) -> bool {
269 Rc::strong_count(&this) == 1
273 impl<T: ?Sized> Rc<T> {
274 /// Downgrades the `Rc<T>` to a `Weak<T>` reference.
281 /// let five = Rc::new(5);
283 /// let weak_five = Rc::downgrade(&five);
285 #[stable(feature = "rc_weak", since = "1.4.0")]
286 pub fn downgrade(this: &Self) -> Weak<T> {
288 Weak { ptr: this.ptr }
291 /// Get the number of weak references to this value.
293 #[unstable(feature = "rc_counts", reason = "not clearly useful",
295 pub fn weak_count(this: &Self) -> usize {
299 /// Get the number of strong references to this value.
301 #[unstable(feature = "rc_counts", reason = "not clearly useful",
303 pub fn strong_count(this: &Self) -> usize {
307 /// Returns true if there are no other `Rc` or `Weak<T>` values that share
308 /// the same inner value.
313 /// #![feature(rc_counts)]
317 /// let five = Rc::new(5);
319 /// assert!(Rc::is_unique(&five));
322 #[unstable(feature = "rc_counts", reason = "uniqueness has unclear meaning",
324 pub fn is_unique(this: &Self) -> bool {
325 Rc::weak_count(this) == 0 && Rc::strong_count(this) == 1
328 /// Returns a mutable reference to the contained value if the `Rc<T>` has
329 /// one strong reference and no weak references.
331 /// Returns `None` if the `Rc<T>` is not unique.
338 /// let mut x = Rc::new(3);
339 /// *Rc::get_mut(&mut x).unwrap() = 4;
340 /// assert_eq!(*x, 4);
342 /// let _y = x.clone();
343 /// assert!(Rc::get_mut(&mut x).is_none());
346 #[stable(feature = "rc_unique", since = "1.4.0")]
347 pub fn get_mut(this: &mut Self) -> Option<&mut T> {
348 if Rc::is_unique(this) {
349 let inner = unsafe { &mut **this.ptr };
350 Some(&mut inner.value)
357 impl<T: Clone> Rc<T> {
358 /// Make a mutable reference into the given `Rc<T>` by cloning the inner
359 /// data if the `Rc<T>` doesn't have one strong reference and no weak
362 /// This is also referred to as a copy-on-write.
369 /// let mut data = Rc::new(5);
371 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
372 /// let mut other_data = data.clone(); // Won't clone inner data
373 /// *Rc::make_mut(&mut data) += 1; // Clones inner data
374 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
375 /// *Rc::make_mut(&mut other_data) *= 2; // Won't clone anything
377 /// // Note: data and other_data now point to different numbers
378 /// assert_eq!(*data, 8);
379 /// assert_eq!(*other_data, 12);
383 #[stable(feature = "rc_unique", since = "1.4.0")]
384 pub fn make_mut(this: &mut Self) -> &mut T {
385 if Rc::strong_count(this) != 1 {
386 // Gotta clone the data, there are other Rcs
387 *this = Rc::new((**this).clone())
388 } else if Rc::weak_count(this) != 0 {
389 // Can just steal the data, all that's left is Weaks
391 let mut swap = Rc::new(ptr::read(&(**this.ptr).value));
392 mem::swap(this, &mut swap);
394 // Remove implicit strong-weak ref (no need to craft a fake
395 // Weak here -- we know other Weaks can clean up for us)
400 // This unsafety is ok because we're guaranteed that the pointer
401 // returned is the *only* pointer that will ever be returned to T. Our
402 // reference count is guaranteed to be 1 at this point, and we required
403 // the `Rc<T>` itself to be `mut`, so we're returning the only possible
404 // reference to the inner value.
405 let inner = unsafe { &mut **this.ptr };
410 #[stable(feature = "rust1", since = "1.0.0")]
411 impl<T: ?Sized> Deref for Rc<T> {
415 fn deref(&self) -> &T {
420 #[stable(feature = "rust1", since = "1.0.0")]
421 impl<T: ?Sized> Drop for Rc<T> {
422 /// Drops the `Rc<T>`.
424 /// This will decrement the strong reference count. If the strong reference
425 /// count becomes zero and the only other references are `Weak<T>` ones,
426 /// `drop`s the inner value.
434 /// let five = Rc::new(5);
438 /// drop(five); // explicit drop
441 /// let five = Rc::new(5);
445 /// } // implicit drop
447 #[unsafe_destructor_blind_to_params]
451 let thin = ptr as *const ();
453 if thin as usize != mem::POST_DROP_USIZE {
455 if self.strong() == 0 {
456 // destroy the contained object
457 ptr::drop_in_place(&mut (*ptr).value);
459 // remove the implicit "strong weak" pointer now that we've
460 // destroyed the contents.
463 if self.weak() == 0 {
464 deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
472 #[stable(feature = "rust1", since = "1.0.0")]
473 impl<T: ?Sized> Clone for Rc<T> {
474 /// Makes a clone of the `Rc<T>`.
476 /// When you clone an `Rc<T>`, it will create another pointer to the data and
477 /// increase the strong reference counter.
484 /// let five = Rc::new(5);
489 fn clone(&self) -> Rc<T> {
495 #[stable(feature = "rust1", since = "1.0.0")]
496 impl<T: Default> Default for Rc<T> {
497 /// Creates a new `Rc<T>`, with the `Default` value for `T`.
504 /// let x: Rc<i32> = Default::default();
507 fn default() -> Rc<T> {
508 Rc::new(Default::default())
512 #[stable(feature = "rust1", since = "1.0.0")]
513 impl<T: ?Sized + PartialEq> PartialEq for Rc<T> {
514 /// Equality for two `Rc<T>`s.
516 /// Two `Rc<T>`s are equal if their inner value are equal.
523 /// let five = Rc::new(5);
525 /// five == Rc::new(5);
528 fn eq(&self, other: &Rc<T>) -> bool {
532 /// Inequality for two `Rc<T>`s.
534 /// Two `Rc<T>`s are unequal if their inner value are unequal.
541 /// let five = Rc::new(5);
543 /// five != Rc::new(5);
546 fn ne(&self, other: &Rc<T>) -> bool {
551 #[stable(feature = "rust1", since = "1.0.0")]
552 impl<T: ?Sized + Eq> Eq for Rc<T> {}
554 #[stable(feature = "rust1", since = "1.0.0")]
555 impl<T: ?Sized + PartialOrd> PartialOrd for Rc<T> {
556 /// Partial comparison for two `Rc<T>`s.
558 /// The two are compared by calling `partial_cmp()` on their inner values.
565 /// let five = Rc::new(5);
567 /// five.partial_cmp(&Rc::new(5));
570 fn partial_cmp(&self, other: &Rc<T>) -> Option<Ordering> {
571 (**self).partial_cmp(&**other)
574 /// Less-than comparison for two `Rc<T>`s.
576 /// The two are compared by calling `<` on their inner values.
583 /// let five = Rc::new(5);
585 /// five < Rc::new(5);
588 fn lt(&self, other: &Rc<T>) -> bool {
592 /// 'Less-than or equal to' comparison for two `Rc<T>`s.
594 /// The two are compared by calling `<=` on their inner values.
601 /// let five = Rc::new(5);
603 /// five <= Rc::new(5);
606 fn le(&self, other: &Rc<T>) -> bool {
610 /// Greater-than comparison for two `Rc<T>`s.
612 /// The two are compared by calling `>` on their inner values.
619 /// let five = Rc::new(5);
621 /// five > Rc::new(5);
624 fn gt(&self, other: &Rc<T>) -> bool {
628 /// 'Greater-than or equal to' comparison for two `Rc<T>`s.
630 /// The two are compared by calling `>=` on their inner values.
637 /// let five = Rc::new(5);
639 /// five >= Rc::new(5);
642 fn ge(&self, other: &Rc<T>) -> bool {
647 #[stable(feature = "rust1", since = "1.0.0")]
648 impl<T: ?Sized + Ord> Ord for Rc<T> {
649 /// Comparison for two `Rc<T>`s.
651 /// The two are compared by calling `cmp()` on their inner values.
658 /// let five = Rc::new(5);
660 /// five.partial_cmp(&Rc::new(5));
663 fn cmp(&self, other: &Rc<T>) -> Ordering {
664 (**self).cmp(&**other)
668 #[stable(feature = "rust1", since = "1.0.0")]
669 impl<T: ?Sized + Hash> Hash for Rc<T> {
670 fn hash<H: Hasher>(&self, state: &mut H) {
671 (**self).hash(state);
675 #[stable(feature = "rust1", since = "1.0.0")]
676 impl<T: ?Sized + fmt::Display> fmt::Display for Rc<T> {
677 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
678 fmt::Display::fmt(&**self, f)
682 #[stable(feature = "rust1", since = "1.0.0")]
683 impl<T: ?Sized + fmt::Debug> fmt::Debug for Rc<T> {
684 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
685 fmt::Debug::fmt(&**self, f)
689 #[stable(feature = "rust1", since = "1.0.0")]
690 impl<T: ?Sized> fmt::Pointer for Rc<T> {
691 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
692 fmt::Pointer::fmt(&*self.ptr, f)
696 #[stable(feature = "from_for_ptrs", since = "1.6.0")]
697 impl<T> From<T> for Rc<T> {
698 fn from(t: T) -> Self {
703 /// A weak version of `Rc<T>`.
705 /// Weak references do not count when determining if the inner value should be
708 /// See the [module level documentation](./index.html) for more.
709 #[unsafe_no_drop_flag]
710 #[stable(feature = "rc_weak", since = "1.4.0")]
711 pub struct Weak<T: ?Sized> {
712 ptr: Shared<RcBox<T>>,
715 #[stable(feature = "rc_weak", since = "1.4.0")]
716 impl<T: ?Sized> !marker::Send for Weak<T> {}
717 #[stable(feature = "rc_weak", since = "1.4.0")]
718 impl<T: ?Sized> !marker::Sync for Weak<T> {}
720 #[unstable(feature = "coerce_unsized", issue = "27732")]
721 impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {}
723 impl<T: ?Sized> Weak<T> {
724 /// Upgrades a weak reference to a strong reference.
726 /// Upgrades the `Weak<T>` reference to an `Rc<T>`, if possible.
728 /// Returns `None` if there were no strong references and the data was
736 /// let five = Rc::new(5);
738 /// let weak_five = Rc::downgrade(&five);
740 /// let strong_five: Option<Rc<_>> = weak_five.upgrade();
742 #[stable(feature = "rc_weak", since = "1.4.0")]
743 pub fn upgrade(&self) -> Option<Rc<T>> {
744 if self.strong() == 0 {
748 Some(Rc { ptr: self.ptr })
753 #[stable(feature = "rc_weak", since = "1.4.0")]
754 impl<T: ?Sized> Drop for Weak<T> {
755 /// Drops the `Weak<T>`.
757 /// This will decrement the weak reference count.
765 /// let five = Rc::new(5);
766 /// let weak_five = Rc::downgrade(&five);
770 /// drop(weak_five); // explicit drop
773 /// let five = Rc::new(5);
774 /// let weak_five = Rc::downgrade(&five);
778 /// } // implicit drop
783 let thin = ptr as *const ();
785 if thin as usize != mem::POST_DROP_USIZE {
787 // the weak count starts at 1, and will only go to zero if all
788 // the strong pointers have disappeared.
789 if self.weak() == 0 {
790 deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
797 #[stable(feature = "rc_weak", since = "1.4.0")]
798 impl<T: ?Sized> Clone for Weak<T> {
799 /// Makes a clone of the `Weak<T>`.
801 /// This increases the weak reference count.
808 /// let weak_five = Rc::downgrade(&Rc::new(5));
810 /// weak_five.clone();
813 fn clone(&self) -> Weak<T> {
815 Weak { ptr: self.ptr }
819 #[stable(feature = "rc_weak", since = "1.4.0")]
820 impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> {
821 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
827 /// Constructs a new `Weak<T>` without an accompanying instance of T.
829 /// This allocates memory for T, but does not initialize it. Calling
830 /// Weak<T>::upgrade() on the return value always gives None.
835 /// #![feature(downgraded_weak)]
837 /// use std::rc::Weak;
839 /// let empty: Weak<i64> = Weak::new();
841 #[unstable(feature = "downgraded_weak",
842 reason = "recently added",
844 pub fn new() -> Weak<T> {
847 ptr: Shared::new(Box::into_raw(box RcBox {
848 strong: Cell::new(0),
850 value: uninitialized(),
857 // NOTE: We checked_add here to deal with mem::forget safety. In particular
858 // if you mem::forget Rcs (or Weaks), the ref-count can overflow, and then
859 // you can free the allocation while outstanding Rcs (or Weaks) exist.
860 // We abort because this is such a degenerate scenario that we don't care about
861 // what happens -- no real program should ever experience this.
863 // This should have negligible overhead since you don't actually need to
864 // clone these much in Rust thanks to ownership and move-semantics.
867 trait RcBoxPtr<T: ?Sized> {
868 fn inner(&self) -> &RcBox<T>;
871 fn strong(&self) -> usize {
872 self.inner().strong.get()
876 fn inc_strong(&self) {
877 self.inner().strong.set(self.strong().checked_add(1).unwrap_or_else(|| unsafe { abort() }));
881 fn dec_strong(&self) {
882 self.inner().strong.set(self.strong() - 1);
886 fn weak(&self) -> usize {
887 self.inner().weak.get()
892 self.inner().weak.set(self.weak().checked_add(1).unwrap_or_else(|| unsafe { abort() }));
897 self.inner().weak.set(self.weak() - 1);
901 impl<T: ?Sized> RcBoxPtr<T> for Rc<T> {
903 fn inner(&self) -> &RcBox<T> {
905 // Safe to assume this here, as if it weren't true, we'd be breaking
906 // the contract anyway.
907 // This allows the null check to be elided in the destructor if we
908 // manipulated the reference count in the same function.
909 assume(!(*(&self.ptr as *const _ as *const *const ())).is_null());
915 impl<T: ?Sized> RcBoxPtr<T> for Weak<T> {
917 fn inner(&self) -> &RcBox<T> {
919 // Safe to assume this here, as if it weren't true, we'd be breaking
920 // the contract anyway.
921 // This allows the null check to be elided in the destructor if we
922 // manipulated the reference count in the same function.
923 assume(!(*(&self.ptr as *const _ as *const *const ())).is_null());
931 use super::{Rc, Weak};
933 use std::cell::RefCell;
934 use std::option::Option;
935 use std::option::Option::{Some, None};
936 use std::result::Result::{Err, Ok};
938 use std::clone::Clone;
939 use std::convert::From;
943 let x = Rc::new(RefCell::new(5));
945 *x.borrow_mut() = 20;
946 assert_eq!(*y.borrow(), 20);
956 fn test_simple_clone() {
964 fn test_destructor() {
965 let x: Rc<Box<_>> = Rc::new(box 5);
972 let y = Rc::downgrade(&x);
973 assert!(y.upgrade().is_some());
979 let y = Rc::downgrade(&x);
981 assert!(y.upgrade().is_none());
985 fn weak_self_cyclic() {
987 x: RefCell<Option<Weak<Cycle>>>,
990 let a = Rc::new(Cycle { x: RefCell::new(None) });
991 let b = Rc::downgrade(&a.clone());
992 *a.x.borrow_mut() = Some(b);
994 // hopefully we don't double-free (or leak)...
1000 assert!(Rc::is_unique(&x));
1002 assert!(!Rc::is_unique(&x));
1004 assert!(Rc::is_unique(&x));
1005 let w = Rc::downgrade(&x);
1006 assert!(!Rc::is_unique(&x));
1008 assert!(Rc::is_unique(&x));
1012 fn test_strong_count() {
1014 assert!(Rc::strong_count(&a) == 1);
1015 let w = Rc::downgrade(&a);
1016 assert!(Rc::strong_count(&a) == 1);
1017 let b = w.upgrade().expect("upgrade of live rc failed");
1018 assert!(Rc::strong_count(&b) == 2);
1019 assert!(Rc::strong_count(&a) == 2);
1022 assert!(Rc::strong_count(&b) == 1);
1024 assert!(Rc::strong_count(&b) == 2);
1025 assert!(Rc::strong_count(&c) == 2);
1029 fn test_weak_count() {
1031 assert!(Rc::strong_count(&a) == 1);
1032 assert!(Rc::weak_count(&a) == 0);
1033 let w = Rc::downgrade(&a);
1034 assert!(Rc::strong_count(&a) == 1);
1035 assert!(Rc::weak_count(&a) == 1);
1037 assert!(Rc::strong_count(&a) == 1);
1038 assert!(Rc::weak_count(&a) == 0);
1040 assert!(Rc::strong_count(&a) == 2);
1041 assert!(Rc::weak_count(&a) == 0);
1048 assert_eq!(Rc::try_unwrap(x), Ok(3));
1051 assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4)));
1053 let _w = Rc::downgrade(&x);
1054 assert_eq!(Rc::try_unwrap(x), Ok(5));
1059 let mut x = Rc::new(3);
1060 *Rc::get_mut(&mut x).unwrap() = 4;
1063 assert!(Rc::get_mut(&mut x).is_none());
1065 assert!(Rc::get_mut(&mut x).is_some());
1066 let _w = Rc::downgrade(&x);
1067 assert!(Rc::get_mut(&mut x).is_none());
1071 fn test_cowrc_clone_make_unique() {
1072 let mut cow0 = Rc::new(75);
1073 let mut cow1 = cow0.clone();
1074 let mut cow2 = cow1.clone();
1076 assert!(75 == *Rc::make_mut(&mut cow0));
1077 assert!(75 == *Rc::make_mut(&mut cow1));
1078 assert!(75 == *Rc::make_mut(&mut cow2));
1080 *Rc::make_mut(&mut cow0) += 1;
1081 *Rc::make_mut(&mut cow1) += 2;
1082 *Rc::make_mut(&mut cow2) += 3;
1084 assert!(76 == *cow0);
1085 assert!(77 == *cow1);
1086 assert!(78 == *cow2);
1088 // none should point to the same backing memory
1089 assert!(*cow0 != *cow1);
1090 assert!(*cow0 != *cow2);
1091 assert!(*cow1 != *cow2);
1095 fn test_cowrc_clone_unique2() {
1096 let mut cow0 = Rc::new(75);
1097 let cow1 = cow0.clone();
1098 let cow2 = cow1.clone();
1100 assert!(75 == *cow0);
1101 assert!(75 == *cow1);
1102 assert!(75 == *cow2);
1104 *Rc::make_mut(&mut cow0) += 1;
1106 assert!(76 == *cow0);
1107 assert!(75 == *cow1);
1108 assert!(75 == *cow2);
1110 // cow1 and cow2 should share the same contents
1111 // cow0 should have a unique reference
1112 assert!(*cow0 != *cow1);
1113 assert!(*cow0 != *cow2);
1114 assert!(*cow1 == *cow2);
1118 fn test_cowrc_clone_weak() {
1119 let mut cow0 = Rc::new(75);
1120 let cow1_weak = Rc::downgrade(&cow0);
1122 assert!(75 == *cow0);
1123 assert!(75 == *cow1_weak.upgrade().unwrap());
1125 *Rc::make_mut(&mut cow0) += 1;
1127 assert!(76 == *cow0);
1128 assert!(cow1_weak.upgrade().is_none());
1133 let foo = Rc::new(75);
1134 assert_eq!(format!("{:?}", foo), "75");
1139 let foo: Rc<[i32]> = Rc::new([1, 2, 3]);
1140 assert_eq!(foo, foo.clone());
1144 fn test_from_owned() {
1146 let foo_rc = Rc::from(foo);
1147 assert!(123 == *foo_rc);
1151 fn test_new_weak() {
1152 let foo: Weak<usize> = Weak::new();
1153 assert!(foo.upgrade().is_none());
1157 #[stable(feature = "rust1", since = "1.0.0")]
1158 impl<T: ?Sized> borrow::Borrow<T> for Rc<T> {
1159 fn borrow(&self) -> &T {
1164 #[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
1165 impl<T: ?Sized> AsRef<T> for Rc<T> {
1166 fn as_ref(&self) -> &T {