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 // FIXME #12808: strange names to try to avoid interfering with field
188 // accesses of the contained type via Deref
189 _ptr: Shared<RcBox<T>>,
192 #[stable(feature = "rust1", since = "1.0.0")]
193 impl<T: ?Sized> !marker::Send for Rc<T> {}
194 #[stable(feature = "rust1", since = "1.0.0")]
195 impl<T: ?Sized> !marker::Sync for Rc<T> {}
197 #[unstable(feature = "coerce_unsized", issue = "27732")]
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 exactly one strong reference.
229 /// Otherwise, an `Err` is returned with the same `Rc<T>`.
231 /// This will succeed even if there are outstanding weak references.
238 /// let x = Rc::new(3);
239 /// assert_eq!(Rc::try_unwrap(x), Ok(3));
241 /// let x = Rc::new(4);
242 /// let _y = x.clone();
243 /// assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4)));
246 #[stable(feature = "rc_unique", since = "1.4.0")]
247 pub fn try_unwrap(this: Self) -> Result<T, Self> {
248 if Rc::would_unwrap(&this) {
250 let val = ptr::read(&*this); // copy the contained object
252 // Indicate to Weaks that they can't be promoted by decrememting
253 // the strong count, and then remove the implicit "strong weak"
254 // pointer while also handling drop logic by just crafting a
257 let _weak = Weak { _ptr: this._ptr };
266 /// Checks if `Rc::try_unwrap` would return `Ok`.
267 #[unstable(feature = "rc_would_unwrap",
268 reason = "just added for niche usecase",
270 pub fn would_unwrap(this: &Self) -> bool {
271 Rc::strong_count(&this) == 1
275 impl<T: ?Sized> Rc<T> {
276 /// Downgrades the `Rc<T>` to a `Weak<T>` reference.
283 /// let five = Rc::new(5);
285 /// let weak_five = Rc::downgrade(&five);
287 #[stable(feature = "rc_weak", since = "1.4.0")]
288 pub fn downgrade(this: &Self) -> Weak<T> {
290 Weak { _ptr: this._ptr }
293 /// Get the number of weak references to this value.
295 #[unstable(feature = "rc_counts", reason = "not clearly useful",
297 pub fn weak_count(this: &Self) -> usize {
301 /// Get the number of strong references to this value.
303 #[unstable(feature = "rc_counts", reason = "not clearly useful",
305 pub fn strong_count(this: &Self) -> usize {
309 /// Returns true if there are no other `Rc` or `Weak<T>` values that share
310 /// the same inner value.
315 /// #![feature(rc_counts)]
319 /// let five = Rc::new(5);
321 /// assert!(Rc::is_unique(&five));
324 #[unstable(feature = "rc_counts", reason = "uniqueness has unclear meaning",
326 pub fn is_unique(this: &Self) -> bool {
327 Rc::weak_count(this) == 0 && Rc::strong_count(this) == 1
330 /// Returns a mutable reference to the contained value if the `Rc<T>` has
331 /// one strong reference and no weak references.
333 /// Returns `None` if the `Rc<T>` is not unique.
340 /// let mut x = Rc::new(3);
341 /// *Rc::get_mut(&mut x).unwrap() = 4;
342 /// assert_eq!(*x, 4);
344 /// let _y = x.clone();
345 /// assert!(Rc::get_mut(&mut x).is_none());
348 #[stable(feature = "rc_unique", since = "1.4.0")]
349 pub fn get_mut(this: &mut Self) -> Option<&mut T> {
350 if Rc::is_unique(this) {
351 let inner = unsafe { &mut **this._ptr };
352 Some(&mut inner.value)
359 impl<T: Clone> Rc<T> {
360 /// Make a mutable reference into the given `Rc<T>` by cloning the inner
361 /// data if the `Rc<T>` doesn't have one strong reference and no weak
364 /// This is also referred to as a copy-on-write.
371 /// let mut data = Rc::new(5);
373 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
374 /// let mut other_data = data.clone(); // Won't clone inner data
375 /// *Rc::make_mut(&mut data) += 1; // Clones inner data
376 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
377 /// *Rc::make_mut(&mut other_data) *= 2; // Won't clone anything
379 /// // Note: data and other_data now point to different numbers
380 /// assert_eq!(*data, 8);
381 /// assert_eq!(*other_data, 12);
385 #[stable(feature = "rc_unique", since = "1.4.0")]
386 pub fn make_mut(this: &mut Self) -> &mut T {
387 if Rc::strong_count(this) != 1 {
388 // Gotta clone the data, there are other Rcs
389 *this = Rc::new((**this).clone())
390 } else if Rc::weak_count(this) != 0 {
391 // Can just steal the data, all that's left is Weaks
393 let mut swap = Rc::new(ptr::read(&(**this._ptr).value));
394 mem::swap(this, &mut swap);
396 // Remove implicit strong-weak ref (no need to craft a fake
397 // Weak here -- we know other Weaks can clean up for us)
402 // This unsafety is ok because we're guaranteed that the pointer
403 // returned is the *only* pointer that will ever be returned to T. Our
404 // reference count is guaranteed to be 1 at this point, and we required
405 // the `Rc<T>` itself to be `mut`, so we're returning the only possible
406 // reference to the inner value.
407 let inner = unsafe { &mut **this._ptr };
412 #[stable(feature = "rust1", since = "1.0.0")]
413 impl<T: ?Sized> Deref for Rc<T> {
417 fn deref(&self) -> &T {
422 #[stable(feature = "rust1", since = "1.0.0")]
423 impl<T: ?Sized> Drop for Rc<T> {
424 /// Drops the `Rc<T>`.
426 /// This will decrement the strong reference count. If the strong reference
427 /// count becomes zero and the only other references are `Weak<T>` ones,
428 /// `drop`s the inner value.
436 /// let five = Rc::new(5);
440 /// drop(five); // explicit drop
443 /// let five = Rc::new(5);
447 /// } // implicit drop
449 #[unsafe_destructor_blind_to_params]
452 let ptr = *self._ptr;
453 let thin = ptr as *const ();
455 if thin as usize != mem::POST_DROP_USIZE {
457 if self.strong() == 0 {
458 // destroy the contained object
459 ptr::drop_in_place(&mut (*ptr).value);
461 // remove the implicit "strong weak" pointer now that we've
462 // destroyed the contents.
465 if self.weak() == 0 {
466 deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
474 #[stable(feature = "rust1", since = "1.0.0")]
475 impl<T: ?Sized> Clone for Rc<T> {
476 /// Makes a clone of the `Rc<T>`.
478 /// When you clone an `Rc<T>`, it will create another pointer to the data and
479 /// increase the strong reference counter.
486 /// let five = Rc::new(5);
491 fn clone(&self) -> Rc<T> {
493 Rc { _ptr: self._ptr }
497 #[stable(feature = "rust1", since = "1.0.0")]
498 impl<T: Default> Default for Rc<T> {
499 /// Creates a new `Rc<T>`, with the `Default` value for `T`.
506 /// let x: Rc<i32> = Default::default();
509 fn default() -> Rc<T> {
510 Rc::new(Default::default())
514 #[stable(feature = "rust1", since = "1.0.0")]
515 impl<T: ?Sized + PartialEq> PartialEq for Rc<T> {
516 /// Equality for two `Rc<T>`s.
518 /// Two `Rc<T>`s are equal if their inner value are equal.
525 /// let five = Rc::new(5);
527 /// five == Rc::new(5);
530 fn eq(&self, other: &Rc<T>) -> bool {
534 /// Inequality for two `Rc<T>`s.
536 /// Two `Rc<T>`s are unequal if their inner value are unequal.
543 /// let five = Rc::new(5);
545 /// five != Rc::new(5);
548 fn ne(&self, other: &Rc<T>) -> bool {
553 #[stable(feature = "rust1", since = "1.0.0")]
554 impl<T: ?Sized + Eq> Eq for Rc<T> {}
556 #[stable(feature = "rust1", since = "1.0.0")]
557 impl<T: ?Sized + PartialOrd> PartialOrd for Rc<T> {
558 /// Partial comparison for two `Rc<T>`s.
560 /// The two are compared by calling `partial_cmp()` on their inner values.
567 /// let five = Rc::new(5);
569 /// five.partial_cmp(&Rc::new(5));
572 fn partial_cmp(&self, other: &Rc<T>) -> Option<Ordering> {
573 (**self).partial_cmp(&**other)
576 /// Less-than comparison for two `Rc<T>`s.
578 /// The two are compared by calling `<` on their inner values.
585 /// let five = Rc::new(5);
587 /// five < Rc::new(5);
590 fn lt(&self, other: &Rc<T>) -> bool {
594 /// 'Less-than or equal to' comparison for two `Rc<T>`s.
596 /// The two are compared by calling `<=` on their inner values.
603 /// let five = Rc::new(5);
605 /// five <= Rc::new(5);
608 fn le(&self, other: &Rc<T>) -> bool {
612 /// Greater-than comparison for two `Rc<T>`s.
614 /// The two are compared by calling `>` on their inner values.
621 /// let five = Rc::new(5);
623 /// five > Rc::new(5);
626 fn gt(&self, other: &Rc<T>) -> bool {
630 /// 'Greater-than or equal to' comparison for two `Rc<T>`s.
632 /// The two are compared by calling `>=` on their inner values.
639 /// let five = Rc::new(5);
641 /// five >= Rc::new(5);
644 fn ge(&self, other: &Rc<T>) -> bool {
649 #[stable(feature = "rust1", since = "1.0.0")]
650 impl<T: ?Sized + Ord> Ord for Rc<T> {
651 /// Comparison for two `Rc<T>`s.
653 /// The two are compared by calling `cmp()` on their inner values.
660 /// let five = Rc::new(5);
662 /// five.partial_cmp(&Rc::new(5));
665 fn cmp(&self, other: &Rc<T>) -> Ordering {
666 (**self).cmp(&**other)
670 #[stable(feature = "rust1", since = "1.0.0")]
671 impl<T: ?Sized + Hash> Hash for Rc<T> {
672 fn hash<H: Hasher>(&self, state: &mut H) {
673 (**self).hash(state);
677 #[stable(feature = "rust1", since = "1.0.0")]
678 impl<T: ?Sized + fmt::Display> fmt::Display for Rc<T> {
679 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
680 fmt::Display::fmt(&**self, f)
684 #[stable(feature = "rust1", since = "1.0.0")]
685 impl<T: ?Sized + fmt::Debug> fmt::Debug for Rc<T> {
686 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
687 fmt::Debug::fmt(&**self, f)
691 #[stable(feature = "rust1", since = "1.0.0")]
692 impl<T: ?Sized> fmt::Pointer for Rc<T> {
693 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
694 fmt::Pointer::fmt(&*self._ptr, f)
698 #[stable(feature = "from_for_ptrs", since = "1.6.0")]
699 impl<T> From<T> for Rc<T> {
700 fn from(t: T) -> Self {
705 /// A weak version of `Rc<T>`.
707 /// Weak references do not count when determining if the inner value should be
710 /// See the [module level documentation](./index.html) for more.
711 #[unsafe_no_drop_flag]
712 #[stable(feature = "rc_weak", since = "1.4.0")]
713 pub struct Weak<T: ?Sized> {
714 // FIXME #12808: strange names to try to avoid interfering with
715 // field accesses of the contained type via Deref
716 _ptr: Shared<RcBox<T>>,
719 #[stable(feature = "rc_weak", since = "1.4.0")]
720 impl<T: ?Sized> !marker::Send for Weak<T> {}
721 #[stable(feature = "rc_weak", since = "1.4.0")]
722 impl<T: ?Sized> !marker::Sync for Weak<T> {}
724 #[unstable(feature = "coerce_unsized", issue = "27732")]
725 impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {}
727 impl<T: ?Sized> Weak<T> {
728 /// Upgrades a weak reference to a strong reference.
730 /// Upgrades the `Weak<T>` reference to an `Rc<T>`, if possible.
732 /// Returns `None` if there were no strong references and the data was
740 /// let five = Rc::new(5);
742 /// let weak_five = Rc::downgrade(&five);
744 /// let strong_five: Option<Rc<_>> = weak_five.upgrade();
746 #[stable(feature = "rc_weak", since = "1.4.0")]
747 pub fn upgrade(&self) -> Option<Rc<T>> {
748 if self.strong() == 0 {
752 Some(Rc { _ptr: self._ptr })
757 #[stable(feature = "rc_weak", since = "1.4.0")]
758 impl<T: ?Sized> Drop for Weak<T> {
759 /// Drops the `Weak<T>`.
761 /// This will decrement the weak reference count.
769 /// let five = Rc::new(5);
770 /// let weak_five = Rc::downgrade(&five);
774 /// drop(weak_five); // explicit drop
777 /// let five = Rc::new(5);
778 /// let weak_five = Rc::downgrade(&five);
782 /// } // implicit drop
786 let ptr = *self._ptr;
787 let thin = ptr as *const ();
789 if thin as usize != mem::POST_DROP_USIZE {
791 // the weak count starts at 1, and will only go to zero if all
792 // the strong pointers have disappeared.
793 if self.weak() == 0 {
794 deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
801 #[stable(feature = "rc_weak", since = "1.4.0")]
802 impl<T: ?Sized> Clone for Weak<T> {
803 /// Makes a clone of the `Weak<T>`.
805 /// This increases the weak reference count.
812 /// let weak_five = Rc::downgrade(&Rc::new(5));
814 /// weak_five.clone();
817 fn clone(&self) -> Weak<T> {
819 Weak { _ptr: self._ptr }
823 #[stable(feature = "rc_weak", since = "1.4.0")]
824 impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> {
825 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
831 /// Constructs a new `Weak<T>` without an accompanying instance of T.
833 /// This allocates memory for T, but does not initialize it. Calling
834 /// Weak<T>::upgrade() on the return value always gives None.
839 /// #![feature(downgraded_weak)]
841 /// use std::rc::Weak;
843 /// let empty: Weak<i64> = Weak::new();
845 #[unstable(feature = "downgraded_weak",
846 reason = "recently added",
848 pub fn new() -> Weak<T> {
851 _ptr: Shared::new(Box::into_raw(box RcBox {
852 strong: Cell::new(0),
854 value: uninitialized(),
861 // NOTE: We checked_add here to deal with mem::forget safety. In particular
862 // if you mem::forget Rcs (or Weaks), the ref-count can overflow, and then
863 // you can free the allocation while outstanding Rcs (or Weaks) exist.
864 // We abort because this is such a degenerate scenario that we don't care about
865 // what happens -- no real program should ever experience this.
867 // This should have negligible overhead since you don't actually need to
868 // clone these much in Rust thanks to ownership and move-semantics.
871 trait RcBoxPtr<T: ?Sized> {
872 fn inner(&self) -> &RcBox<T>;
875 fn strong(&self) -> usize {
876 self.inner().strong.get()
880 fn inc_strong(&self) {
881 self.inner().strong.set(self.strong().checked_add(1).unwrap_or_else(|| unsafe { abort() }));
885 fn dec_strong(&self) {
886 self.inner().strong.set(self.strong() - 1);
890 fn weak(&self) -> usize {
891 self.inner().weak.get()
896 self.inner().weak.set(self.weak().checked_add(1).unwrap_or_else(|| unsafe { abort() }));
901 self.inner().weak.set(self.weak() - 1);
905 impl<T: ?Sized> RcBoxPtr<T> for Rc<T> {
907 fn inner(&self) -> &RcBox<T> {
909 // Safe to assume this here, as if it weren't true, we'd be breaking
910 // the contract anyway.
911 // This allows the null check to be elided in the destructor if we
912 // manipulated the reference count in the same function.
913 assume(!(*(&self._ptr as *const _ as *const *const ())).is_null());
919 impl<T: ?Sized> RcBoxPtr<T> for Weak<T> {
921 fn inner(&self) -> &RcBox<T> {
923 // Safe to assume this here, as if it weren't true, we'd be breaking
924 // the contract anyway.
925 // This allows the null check to be elided in the destructor if we
926 // manipulated the reference count in the same function.
927 assume(!(*(&self._ptr as *const _ as *const *const ())).is_null());
935 use super::{Rc, Weak};
937 use std::cell::RefCell;
938 use std::option::Option;
939 use std::option::Option::{Some, None};
940 use std::result::Result::{Err, Ok};
942 use std::clone::Clone;
943 use std::convert::From;
947 let x = Rc::new(RefCell::new(5));
949 *x.borrow_mut() = 20;
950 assert_eq!(*y.borrow(), 20);
960 fn test_simple_clone() {
968 fn test_destructor() {
969 let x: Rc<Box<_>> = Rc::new(box 5);
976 let y = Rc::downgrade(&x);
977 assert!(y.upgrade().is_some());
983 let y = Rc::downgrade(&x);
985 assert!(y.upgrade().is_none());
989 fn weak_self_cyclic() {
991 x: RefCell<Option<Weak<Cycle>>>,
994 let a = Rc::new(Cycle { x: RefCell::new(None) });
995 let b = Rc::downgrade(&a.clone());
996 *a.x.borrow_mut() = Some(b);
998 // hopefully we don't double-free (or leak)...
1004 assert!(Rc::is_unique(&x));
1006 assert!(!Rc::is_unique(&x));
1008 assert!(Rc::is_unique(&x));
1009 let w = Rc::downgrade(&x);
1010 assert!(!Rc::is_unique(&x));
1012 assert!(Rc::is_unique(&x));
1016 fn test_strong_count() {
1018 assert!(Rc::strong_count(&a) == 1);
1019 let w = Rc::downgrade(&a);
1020 assert!(Rc::strong_count(&a) == 1);
1021 let b = w.upgrade().expect("upgrade of live rc failed");
1022 assert!(Rc::strong_count(&b) == 2);
1023 assert!(Rc::strong_count(&a) == 2);
1026 assert!(Rc::strong_count(&b) == 1);
1028 assert!(Rc::strong_count(&b) == 2);
1029 assert!(Rc::strong_count(&c) == 2);
1033 fn test_weak_count() {
1035 assert!(Rc::strong_count(&a) == 1);
1036 assert!(Rc::weak_count(&a) == 0);
1037 let w = Rc::downgrade(&a);
1038 assert!(Rc::strong_count(&a) == 1);
1039 assert!(Rc::weak_count(&a) == 1);
1041 assert!(Rc::strong_count(&a) == 1);
1042 assert!(Rc::weak_count(&a) == 0);
1044 assert!(Rc::strong_count(&a) == 2);
1045 assert!(Rc::weak_count(&a) == 0);
1052 assert_eq!(Rc::try_unwrap(x), Ok(3));
1055 assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4)));
1057 let _w = Rc::downgrade(&x);
1058 assert_eq!(Rc::try_unwrap(x), Ok(5));
1063 let mut x = Rc::new(3);
1064 *Rc::get_mut(&mut x).unwrap() = 4;
1067 assert!(Rc::get_mut(&mut x).is_none());
1069 assert!(Rc::get_mut(&mut x).is_some());
1070 let _w = Rc::downgrade(&x);
1071 assert!(Rc::get_mut(&mut x).is_none());
1075 fn test_cowrc_clone_make_unique() {
1076 let mut cow0 = Rc::new(75);
1077 let mut cow1 = cow0.clone();
1078 let mut cow2 = cow1.clone();
1080 assert!(75 == *Rc::make_mut(&mut cow0));
1081 assert!(75 == *Rc::make_mut(&mut cow1));
1082 assert!(75 == *Rc::make_mut(&mut cow2));
1084 *Rc::make_mut(&mut cow0) += 1;
1085 *Rc::make_mut(&mut cow1) += 2;
1086 *Rc::make_mut(&mut cow2) += 3;
1088 assert!(76 == *cow0);
1089 assert!(77 == *cow1);
1090 assert!(78 == *cow2);
1092 // none should point to the same backing memory
1093 assert!(*cow0 != *cow1);
1094 assert!(*cow0 != *cow2);
1095 assert!(*cow1 != *cow2);
1099 fn test_cowrc_clone_unique2() {
1100 let mut cow0 = Rc::new(75);
1101 let cow1 = cow0.clone();
1102 let cow2 = cow1.clone();
1104 assert!(75 == *cow0);
1105 assert!(75 == *cow1);
1106 assert!(75 == *cow2);
1108 *Rc::make_mut(&mut cow0) += 1;
1110 assert!(76 == *cow0);
1111 assert!(75 == *cow1);
1112 assert!(75 == *cow2);
1114 // cow1 and cow2 should share the same contents
1115 // cow0 should have a unique reference
1116 assert!(*cow0 != *cow1);
1117 assert!(*cow0 != *cow2);
1118 assert!(*cow1 == *cow2);
1122 fn test_cowrc_clone_weak() {
1123 let mut cow0 = Rc::new(75);
1124 let cow1_weak = Rc::downgrade(&cow0);
1126 assert!(75 == *cow0);
1127 assert!(75 == *cow1_weak.upgrade().unwrap());
1129 *Rc::make_mut(&mut cow0) += 1;
1131 assert!(76 == *cow0);
1132 assert!(cow1_weak.upgrade().is_none());
1137 let foo = Rc::new(75);
1138 assert_eq!(format!("{:?}", foo), "75");
1143 let foo: Rc<[i32]> = Rc::new([1, 2, 3]);
1144 assert_eq!(foo, foo.clone());
1148 fn test_from_owned() {
1150 let foo_rc = Rc::from(foo);
1151 assert!(123 == *foo_rc);
1155 fn test_new_weak() {
1156 let foo: Weak<usize> = Weak::new();
1157 assert!(foo.upgrade().is_none());
1161 #[stable(feature = "rust1", since = "1.0.0")]
1162 impl<T: ?Sized> borrow::Borrow<T> for Rc<T> {
1163 fn borrow(&self) -> &T {
1168 #[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
1169 impl<T: ?Sized> AsRef<T> for Rc<T> {
1170 fn as_ref(&self) -> &T {