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};
173 use heap::deallocate;
175 struct RcBox<T: ?Sized> {
182 /// A reference-counted pointer type over an immutable value.
184 /// See the [module level documentation](./index.html) for more details.
185 #[unsafe_no_drop_flag]
186 #[stable(feature = "rust1", since = "1.0.0")]
187 pub struct Rc<T: ?Sized> {
188 // FIXME #12808: strange names to try to avoid interfering with field
189 // accesses of the contained type via Deref
190 _ptr: Shared<RcBox<T>>,
193 impl<T: ?Sized> !marker::Send for Rc<T> {}
194 impl<T: ?Sized> !marker::Sync for Rc<T> {}
196 #[cfg(not(stage0))] // remove cfg after new snapshot
197 impl<T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<Rc<U>> for Rc<T> {}
200 /// Constructs a new `Rc<T>`.
207 /// let five = Rc::new(5);
209 #[stable(feature = "rust1", since = "1.0.0")]
210 pub fn new(value: T) -> Rc<T> {
213 // there is an implicit weak pointer owned by all the strong
214 // pointers, which ensures that the weak destructor never frees
215 // the allocation while the strong destructor is running, even
216 // if the weak pointer is stored inside the strong one.
217 _ptr: Shared::new(Box::into_raw(box RcBox {
218 strong: Cell::new(1),
226 /// Unwraps the contained value if the `Rc<T>` has only one strong reference.
227 /// This will succeed even if there are outstanding weak references.
229 /// Otherwise, an `Err` is returned with the same `Rc<T>`.
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> {
359 #[unstable(feature = "rc_make_unique", reason = "renamed to Rc::make_mut",
361 #[deprecated(since = "1.4.0", reason = "renamed to Rc::make_mut")]
362 pub fn make_unique(&mut self) -> &mut T {
366 /// Make a mutable reference into the given `Rc<T>` by cloning the inner
367 /// data if the `Rc<T>` doesn't have one strong reference and no weak
370 /// This is also referred to as a copy-on-write.
377 /// let mut data = Rc::new(5);
379 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
380 /// let mut other_data = data.clone(); // Won't clone inner data
381 /// *Rc::make_mut(&mut data) += 1; // Clones inner data
382 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
383 /// *Rc::make_mut(&mut other_data) *= 2; // Won't clone anything
385 /// // Note: data and other_data now point to different numbers
386 /// assert_eq!(*data, 8);
387 /// assert_eq!(*other_data, 12);
391 #[stable(feature = "rc_unique", since = "1.4.0")]
392 pub fn make_mut(this: &mut Self) -> &mut T {
393 if Rc::strong_count(this) != 1 {
394 // Gotta clone the data, there are other Rcs
395 *this = Rc::new((**this).clone())
396 } else if Rc::weak_count(this) != 0 {
397 // Can just steal the data, all that's left is Weaks
399 let mut swap = Rc::new(ptr::read(&(**this._ptr).value));
400 mem::swap(this, &mut swap);
402 // Remove implicit strong-weak ref (no need to craft a fake
403 // Weak here -- we know other Weaks can clean up for us)
408 // This unsafety is ok because we're guaranteed that the pointer
409 // returned is the *only* pointer that will ever be returned to T. Our
410 // reference count is guaranteed to be 1 at this point, and we required
411 // the `Rc<T>` itself to be `mut`, so we're returning the only possible
412 // reference to the inner value.
413 let inner = unsafe { &mut **this._ptr };
418 #[stable(feature = "rust1", since = "1.0.0")]
419 impl<T: ?Sized> Deref for Rc<T> {
423 fn deref(&self) -> &T {
428 #[stable(feature = "rust1", since = "1.0.0")]
429 impl<T: ?Sized> Drop for Rc<T> {
430 /// Drops the `Rc<T>`.
432 /// This will decrement the strong reference count. If the strong reference
433 /// count becomes zero and the only other references are `Weak<T>` ones,
434 /// `drop`s the inner value.
442 /// let five = Rc::new(5);
446 /// drop(five); // explicit drop
449 /// let five = Rc::new(5);
453 /// } // implicit drop
455 #[unsafe_destructor_blind_to_params]
458 let ptr = *self._ptr;
459 if !(*(&ptr as *const _ as *const *const ())).is_null() &&
460 ptr as *const () as usize != mem::POST_DROP_USIZE {
462 if self.strong() == 0 {
463 // destroy the contained object
464 ptr::drop_in_place(&mut (*ptr).value);
466 // remove the implicit "strong weak" pointer now that we've
467 // destroyed the contents.
470 if self.weak() == 0 {
471 deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
479 #[stable(feature = "rust1", since = "1.0.0")]
480 impl<T: ?Sized> Clone for Rc<T> {
482 /// Makes a clone of the `Rc<T>`.
484 /// When you clone an `Rc<T>`, it will create another pointer to the data and
485 /// increase the strong reference counter.
492 /// let five = Rc::new(5);
497 fn clone(&self) -> Rc<T> {
499 Rc { _ptr: self._ptr }
503 #[stable(feature = "rust1", since = "1.0.0")]
504 impl<T: Default> Default for Rc<T> {
505 /// Creates a new `Rc<T>`, with the `Default` value for `T`.
512 /// let x: Rc<i32> = Default::default();
515 fn default() -> Rc<T> {
516 Rc::new(Default::default())
520 #[stable(feature = "rust1", since = "1.0.0")]
521 impl<T: ?Sized + PartialEq> PartialEq for Rc<T> {
522 /// Equality for two `Rc<T>`s.
524 /// Two `Rc<T>`s are equal if their inner value are equal.
531 /// let five = Rc::new(5);
533 /// five == Rc::new(5);
536 fn eq(&self, other: &Rc<T>) -> bool {
540 /// Inequality for two `Rc<T>`s.
542 /// Two `Rc<T>`s are unequal if their inner value are unequal.
549 /// let five = Rc::new(5);
551 /// five != Rc::new(5);
554 fn ne(&self, other: &Rc<T>) -> bool {
559 #[stable(feature = "rust1", since = "1.0.0")]
560 impl<T: ?Sized + Eq> Eq for Rc<T> {}
562 #[stable(feature = "rust1", since = "1.0.0")]
563 impl<T: ?Sized + PartialOrd> PartialOrd for Rc<T> {
564 /// Partial comparison for two `Rc<T>`s.
566 /// The two are compared by calling `partial_cmp()` on their inner values.
573 /// let five = Rc::new(5);
575 /// five.partial_cmp(&Rc::new(5));
578 fn partial_cmp(&self, other: &Rc<T>) -> Option<Ordering> {
579 (**self).partial_cmp(&**other)
582 /// Less-than comparison for two `Rc<T>`s.
584 /// The two are compared by calling `<` on their inner values.
591 /// let five = Rc::new(5);
593 /// five < Rc::new(5);
596 fn lt(&self, other: &Rc<T>) -> bool {
600 /// 'Less-than or equal to' comparison for two `Rc<T>`s.
602 /// The two are compared by calling `<=` on their inner values.
609 /// let five = Rc::new(5);
611 /// five <= Rc::new(5);
614 fn le(&self, other: &Rc<T>) -> bool {
618 /// Greater-than comparison for two `Rc<T>`s.
620 /// The two are compared by calling `>` on their inner values.
627 /// let five = Rc::new(5);
629 /// five > Rc::new(5);
632 fn gt(&self, other: &Rc<T>) -> bool {
636 /// 'Greater-than or equal to' comparison for two `Rc<T>`s.
638 /// The two are compared by calling `>=` on their inner values.
645 /// let five = Rc::new(5);
647 /// five >= Rc::new(5);
650 fn ge(&self, other: &Rc<T>) -> bool {
655 #[stable(feature = "rust1", since = "1.0.0")]
656 impl<T: ?Sized + Ord> Ord for Rc<T> {
657 /// Comparison for two `Rc<T>`s.
659 /// The two are compared by calling `cmp()` on their inner values.
666 /// let five = Rc::new(5);
668 /// five.partial_cmp(&Rc::new(5));
671 fn cmp(&self, other: &Rc<T>) -> Ordering {
672 (**self).cmp(&**other)
676 #[stable(feature = "rust1", since = "1.0.0")]
677 impl<T: ?Sized+Hash> Hash for Rc<T> {
678 fn hash<H: Hasher>(&self, state: &mut H) {
679 (**self).hash(state);
683 #[stable(feature = "rust1", since = "1.0.0")]
684 impl<T: ?Sized+fmt::Display> fmt::Display for Rc<T> {
685 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
686 fmt::Display::fmt(&**self, f)
690 #[stable(feature = "rust1", since = "1.0.0")]
691 impl<T: ?Sized+fmt::Debug> fmt::Debug for Rc<T> {
692 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
693 fmt::Debug::fmt(&**self, f)
697 #[stable(feature = "rust1", since = "1.0.0")]
698 impl<T> fmt::Pointer for Rc<T> {
699 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
700 fmt::Pointer::fmt(&*self._ptr, f)
704 /// A weak version of `Rc<T>`.
706 /// Weak references do not count when determining if the inner value should be
709 /// See the [module level documentation](./index.html) for more.
710 #[unsafe_no_drop_flag]
711 #[stable(feature = "rc_weak", since = "1.4.0")]
712 pub struct Weak<T: ?Sized> {
713 // FIXME #12808: strange names to try to avoid interfering with
714 // field accesses of the contained type via Deref
715 _ptr: Shared<RcBox<T>>,
718 impl<T: ?Sized> !marker::Send for Weak<T> {}
719 impl<T: ?Sized> !marker::Sync for Weak<T> {}
721 #[cfg(not(stage0))] // remove cfg after new snapshot
722 impl<T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {}
724 impl<T: ?Sized> Weak<T> {
725 /// Upgrades a weak reference to a strong reference.
727 /// Upgrades the `Weak<T>` reference to an `Rc<T>`, if possible.
729 /// Returns `None` if there were no strong references and the data was
737 /// let five = Rc::new(5);
739 /// let weak_five = Rc::downgrade(&five);
741 /// let strong_five: Option<Rc<_>> = weak_five.upgrade();
743 #[stable(feature = "rc_weak", since = "1.4.0")]
744 pub fn upgrade(&self) -> Option<Rc<T>> {
745 if self.strong() == 0 {
749 Some(Rc { _ptr: self._ptr })
754 #[stable(feature = "rust1", since = "1.0.0")]
755 impl<T: ?Sized> Drop for Weak<T> {
756 /// Drops the `Weak<T>`.
758 /// This will decrement the weak reference count.
766 /// let five = Rc::new(5);
767 /// let weak_five = Rc::downgrade(&five);
771 /// drop(weak_five); // explicit drop
774 /// let five = Rc::new(5);
775 /// let weak_five = Rc::downgrade(&five);
779 /// } // implicit drop
783 let ptr = *self._ptr;
784 if !(*(&ptr as *const _ as *const *const ())).is_null() &&
785 ptr as *const () 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> {
800 /// Makes a clone of the `Weak<T>`.
802 /// This increases the weak reference count.
809 /// let weak_five = Rc::downgrade(&Rc::new(5));
811 /// weak_five.clone();
814 fn clone(&self) -> Weak<T> {
816 Weak { _ptr: self._ptr }
820 #[stable(feature = "rust1", since = "1.0.0")]
821 impl<T: ?Sized+fmt::Debug> fmt::Debug for Weak<T> {
822 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
827 // NOTE: We checked_add here to deal with mem::forget safety. In particular
828 // if you mem::forget Rcs (or Weaks), the ref-count can overflow, and then
829 // you can free the allocation while outstanding Rcs (or Weaks) exist.
830 // We abort because this is such a degenerate scenario that we don't care about
831 // what happens -- no real program should ever experience this.
833 // This should have negligible overhead since you don't actually need to
834 // clone these much in Rust thanks to ownership and move-semantics.
837 trait RcBoxPtr<T: ?Sized> {
838 fn inner(&self) -> &RcBox<T>;
841 fn strong(&self) -> usize {
842 self.inner().strong.get()
846 fn inc_strong(&self) {
847 self.inner().strong.set(self.strong().checked_add(1).unwrap_or_else(|| unsafe { abort() }));
851 fn dec_strong(&self) {
852 self.inner().strong.set(self.strong() - 1);
856 fn weak(&self) -> usize {
857 self.inner().weak.get()
862 self.inner().weak.set(self.weak().checked_add(1).unwrap_or_else(|| unsafe { abort() }));
867 self.inner().weak.set(self.weak() - 1);
871 impl<T: ?Sized> RcBoxPtr<T> for Rc<T> {
873 fn inner(&self) -> &RcBox<T> {
875 // Safe to assume this here, as if it weren't true, we'd be breaking
876 // the contract anyway.
877 // This allows the null check to be elided in the destructor if we
878 // manipulated the reference count in the same function.
879 assume(!(*(&self._ptr as *const _ as *const *const ())).is_null());
885 impl<T: ?Sized> RcBoxPtr<T> for Weak<T> {
887 fn inner(&self) -> &RcBox<T> {
889 // Safe to assume this here, as if it weren't true, we'd be breaking
890 // the contract anyway.
891 // This allows the null check to be elided in the destructor if we
892 // manipulated the reference count in the same function.
893 assume(!(*(&self._ptr as *const _ as *const *const ())).is_null());
901 use super::{Rc, Weak};
903 use std::cell::RefCell;
904 use std::option::Option;
905 use std::option::Option::{Some, None};
906 use std::result::Result::{Err, Ok};
908 use std::clone::Clone;
912 let x = Rc::new(RefCell::new(5));
914 *x.borrow_mut() = 20;
915 assert_eq!(*y.borrow(), 20);
925 fn test_simple_clone() {
933 fn test_destructor() {
934 let x: Rc<Box<_>> = Rc::new(box 5);
941 let y = Rc::downgrade(&x);
942 assert!(y.upgrade().is_some());
948 let y = Rc::downgrade(&x);
950 assert!(y.upgrade().is_none());
954 fn weak_self_cyclic() {
956 x: RefCell<Option<Weak<Cycle>>>,
959 let a = Rc::new(Cycle { x: RefCell::new(None) });
960 let b = Rc::downgrade(&a.clone());
961 *a.x.borrow_mut() = Some(b);
963 // hopefully we don't double-free (or leak)...
969 assert!(Rc::is_unique(&x));
971 assert!(!Rc::is_unique(&x));
973 assert!(Rc::is_unique(&x));
974 let w = Rc::downgrade(&x);
975 assert!(!Rc::is_unique(&x));
977 assert!(Rc::is_unique(&x));
981 fn test_strong_count() {
982 let a = Rc::new(0u32);
983 assert!(Rc::strong_count(&a) == 1);
984 let w = Rc::downgrade(&a);
985 assert!(Rc::strong_count(&a) == 1);
986 let b = w.upgrade().expect("upgrade of live rc failed");
987 assert!(Rc::strong_count(&b) == 2);
988 assert!(Rc::strong_count(&a) == 2);
991 assert!(Rc::strong_count(&b) == 1);
993 assert!(Rc::strong_count(&b) == 2);
994 assert!(Rc::strong_count(&c) == 2);
998 fn test_weak_count() {
999 let a = Rc::new(0u32);
1000 assert!(Rc::strong_count(&a) == 1);
1001 assert!(Rc::weak_count(&a) == 0);
1002 let w = Rc::downgrade(&a);
1003 assert!(Rc::strong_count(&a) == 1);
1004 assert!(Rc::weak_count(&a) == 1);
1006 assert!(Rc::strong_count(&a) == 1);
1007 assert!(Rc::weak_count(&a) == 0);
1009 assert!(Rc::strong_count(&a) == 2);
1010 assert!(Rc::weak_count(&a) == 0);
1017 assert_eq!(Rc::try_unwrap(x), Ok(3));
1020 assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4)));
1022 let _w = Rc::downgrade(&x);
1023 assert_eq!(Rc::try_unwrap(x), Ok(5));
1028 let mut x = Rc::new(3);
1029 *Rc::get_mut(&mut x).unwrap() = 4;
1032 assert!(Rc::get_mut(&mut x).is_none());
1034 assert!(Rc::get_mut(&mut x).is_some());
1035 let _w = Rc::downgrade(&x);
1036 assert!(Rc::get_mut(&mut x).is_none());
1040 fn test_cowrc_clone_make_unique() {
1041 let mut cow0 = Rc::new(75);
1042 let mut cow1 = cow0.clone();
1043 let mut cow2 = cow1.clone();
1045 assert!(75 == *Rc::make_mut(&mut cow0));
1046 assert!(75 == *Rc::make_mut(&mut cow1));
1047 assert!(75 == *Rc::make_mut(&mut cow2));
1049 *Rc::make_mut(&mut cow0) += 1;
1050 *Rc::make_mut(&mut cow1) += 2;
1051 *Rc::make_mut(&mut cow2) += 3;
1053 assert!(76 == *cow0);
1054 assert!(77 == *cow1);
1055 assert!(78 == *cow2);
1057 // none should point to the same backing memory
1058 assert!(*cow0 != *cow1);
1059 assert!(*cow0 != *cow2);
1060 assert!(*cow1 != *cow2);
1064 fn test_cowrc_clone_unique2() {
1065 let mut cow0 = Rc::new(75);
1066 let cow1 = cow0.clone();
1067 let cow2 = cow1.clone();
1069 assert!(75 == *cow0);
1070 assert!(75 == *cow1);
1071 assert!(75 == *cow2);
1073 *Rc::make_mut(&mut cow0) += 1;
1075 assert!(76 == *cow0);
1076 assert!(75 == *cow1);
1077 assert!(75 == *cow2);
1079 // cow1 and cow2 should share the same contents
1080 // cow0 should have a unique reference
1081 assert!(*cow0 != *cow1);
1082 assert!(*cow0 != *cow2);
1083 assert!(*cow1 == *cow2);
1087 fn test_cowrc_clone_weak() {
1088 let mut cow0 = Rc::new(75);
1089 let cow1_weak = Rc::downgrade(&cow0);
1091 assert!(75 == *cow0);
1092 assert!(75 == *cow1_weak.upgrade().unwrap());
1094 *Rc::make_mut(&mut cow0) += 1;
1096 assert!(76 == *cow0);
1097 assert!(cow1_weak.upgrade().is_none());
1102 let foo = Rc::new(75);
1103 assert_eq!(format!("{:?}", foo), "75");
1108 let foo: Rc<[i32]> = Rc::new([1, 2, 3]);
1109 assert_eq!(foo, foo.clone());
1113 impl<T: ?Sized> borrow::Borrow<T> for Rc<T> {
1114 fn borrow(&self) -> &T {
1119 #[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
1120 impl<T: ?Sized> AsRef<T> for Rc<T> {
1121 fn as_ref(&self) -> &T {