1 // Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
13 //! Thread-local reference-counted boxes (the `Rc<T>` type).
15 //! The `Rc<T>` type provides shared ownership of an immutable value.
16 //! Destruction is deterministic, and will occur as soon as the last owner is
17 //! gone. It is marked as non-sendable because it avoids the overhead of atomic
18 //! reference counting.
20 //! The `downgrade` method can be used to create a non-owning `Weak<T>` pointer
21 //! to the box. A `Weak<T>` pointer can be upgraded to an `Rc<T>` pointer, but
22 //! will return `None` if the value has already been dropped.
24 //! For example, a tree with parent pointers can be represented by putting the
25 //! nodes behind strong `Rc<T>` pointers, and then storing the parent pointers
26 //! as `Weak<T>` pointers.
30 //! Consider a scenario where a set of `Gadget`s are owned by a given `Owner`.
31 //! We want to have our `Gadget`s point to their `Owner`. We can't do this with
32 //! unique ownership, because more than one gadget may belong to the same
33 //! `Owner`. `Rc<T>` allows us to share an `Owner` between multiple `Gadget`s,
34 //! and have the `Owner` remain allocated as long as any `Gadget` points at it.
41 //! // ...other fields
47 //! // ...other fields
51 //! // Create a reference counted Owner.
52 //! let gadget_owner : Rc<Owner> = Rc::new(
53 //! Owner { name: String::from("Gadget Man") }
56 //! // Create Gadgets belonging to gadget_owner. To increment the reference
57 //! // count we clone the `Rc<T>` object.
58 //! let gadget1 = Gadget { id: 1, owner: gadget_owner.clone() };
59 //! let gadget2 = Gadget { id: 2, owner: gadget_owner.clone() };
61 //! drop(gadget_owner);
63 //! // Despite dropping gadget_owner, we're still able to print out the name
64 //! // of the Owner of the Gadgets. This is because we've only dropped the
65 //! // reference count object, not the Owner it wraps. As long as there are
66 //! // other `Rc<T>` objects pointing at the same Owner, it will remain
67 //! // allocated. Notice that the `Rc<T>` wrapper around Gadget.owner gets
68 //! // automatically dereferenced for us.
69 //! println!("Gadget {} owned by {}", gadget1.id, gadget1.owner.name);
70 //! println!("Gadget {} owned by {}", gadget2.id, gadget2.owner.name);
72 //! // At the end of the method, gadget1 and gadget2 get destroyed, and with
73 //! // them the last counted references to our Owner. Gadget Man now gets
74 //! // destroyed as well.
78 //! If our requirements change, and we also need to be able to traverse from
79 //! Owner → Gadget, we will run into problems: an `Rc<T>` pointer from Owner
80 //! → Gadget introduces a cycle between the objects. This means that their
81 //! reference counts can never reach 0, and the objects will remain allocated: a
82 //! memory leak. In order to get around this, we can use `Weak<T>` pointers.
83 //! These pointers don't contribute to the total count.
85 //! Rust actually makes it somewhat difficult to produce this loop in the first
86 //! place: in order to end up with two objects that point at each other, one of
87 //! them needs to be mutable. This is problematic because `Rc<T>` enforces
88 //! memory safety by only giving out shared references to the object it wraps,
89 //! and these don't allow direct mutation. We need to wrap the part of the
90 //! object we wish to mutate in a `RefCell`, which provides *interior
91 //! mutability*: a method to achieve mutability through a shared reference.
92 //! `RefCell` enforces Rust's borrowing rules at runtime. Read the `Cell`
93 //! documentation for more details on interior mutability.
97 //! use std::rc::Weak;
98 //! use std::cell::RefCell;
102 //! gadgets: RefCell<Vec<Weak<Gadget>>>,
103 //! // ...other fields
108 //! owner: Rc<Owner>,
109 //! // ...other fields
113 //! // Create a reference counted Owner. Note the fact that we've put the
114 //! // Owner's vector of Gadgets inside a RefCell so that we can mutate it
115 //! // through a shared reference.
116 //! let gadget_owner : Rc<Owner> = Rc::new(
118 //! name: "Gadget Man".to_string(),
119 //! gadgets: RefCell::new(Vec::new()),
123 //! // Create Gadgets belonging to gadget_owner as before.
124 //! let gadget1 = Rc::new(Gadget{id: 1, owner: gadget_owner.clone()});
125 //! let gadget2 = Rc::new(Gadget{id: 2, owner: gadget_owner.clone()});
127 //! // Add the Gadgets to their Owner. To do this we mutably borrow from
128 //! // the RefCell holding the Owner's Gadgets.
129 //! gadget_owner.gadgets.borrow_mut().push(Rc::downgrade(&gadget1));
130 //! gadget_owner.gadgets.borrow_mut().push(Rc::downgrade(&gadget2));
132 //! // Iterate over our Gadgets, printing their details out
133 //! for gadget_opt in gadget_owner.gadgets.borrow().iter() {
135 //! // gadget_opt is a Weak<Gadget>. Since weak pointers can't guarantee
136 //! // that their object is still allocated, we need to call upgrade()
137 //! // on them to turn them into a strong reference. This returns an
138 //! // Option, which contains a reference to our object if it still
140 //! let gadget = gadget_opt.upgrade().unwrap();
141 //! println!("Gadget {} owned by {}", gadget.id, gadget.owner.name);
144 //! // At the end of the method, gadget_owner, gadget1 and gadget2 get
145 //! // destroyed. There are now no strong (`Rc<T>`) references to the gadgets.
146 //! // Once they get destroyed, the Gadgets get destroyed. This zeroes the
147 //! // reference count on Gadget Man, they get destroyed as well.
151 #![stable(feature = "rust1", since = "1.0.0")]
159 use core
::cell
::Cell
;
160 use core
::cmp
::Ordering
;
162 use core
::hash
::{Hasher, Hash}
;
163 use core
::intrinsics
::{assume, abort}
;
166 use core
::marker
::Unsize
;
167 use core
::mem
::{self, align_of_val, size_of_val, forget}
;
168 use core
::ops
::Deref
;
170 use core
::ops
::CoerceUnsized
;
171 use core
::ptr
::{self, Shared}
;
172 use core
::convert
::From
;
174 use heap
::deallocate
;
176 struct RcBox
<T
: ?Sized
> {
183 /// A reference-counted pointer type over an immutable value.
185 /// See the [module level documentation](./index.html) for more details.
186 #[unsafe_no_drop_flag]
187 #[stable(feature = "rust1", since = "1.0.0")]
188 pub struct Rc
<T
: ?Sized
> {
189 // FIXME #12808: strange names to try to avoid interfering with field
190 // accesses of the contained type via Deref
191 _ptr
: Shared
<RcBox
<T
>>,
194 #[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
> {
364 #[unstable(feature = "rc_make_unique", reason = "renamed to Rc::make_mut",
366 #[rustc_deprecated(since = "1.4.0", reason = "renamed to Rc::make_mut")]
367 pub fn make_unique(&mut self) -> &mut T
{
371 /// Make a mutable reference into the given `Rc<T>` by cloning the inner
372 /// data if the `Rc<T>` doesn't have one strong reference and no weak
375 /// This is also referred to as a copy-on-write.
382 /// let mut data = Rc::new(5);
384 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
385 /// let mut other_data = data.clone(); // Won't clone inner data
386 /// *Rc::make_mut(&mut data) += 1; // Clones inner data
387 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
388 /// *Rc::make_mut(&mut other_data) *= 2; // Won't clone anything
390 /// // Note: data and other_data now point to different numbers
391 /// assert_eq!(*data, 8);
392 /// assert_eq!(*other_data, 12);
396 #[stable(feature = "rc_unique", since = "1.4.0")]
397 pub fn make_mut(this
: &mut Self) -> &mut T
{
398 if Rc
::strong_count(this
) != 1 {
399 // Gotta clone the data, there are other Rcs
400 *this
= Rc
::new((**this
).clone())
401 } else if Rc
::weak_count(this
) != 0 {
402 // Can just steal the data, all that's left is Weaks
404 let mut swap
= Rc
::new(ptr
::read(&(**this
._ptr
).value
));
405 mem
::swap(this
, &mut swap
);
407 // Remove implicit strong-weak ref (no need to craft a fake
408 // Weak here -- we know other Weaks can clean up for us)
413 // This unsafety is ok because we're guaranteed that the pointer
414 // returned is the *only* pointer that will ever be returned to T. Our
415 // reference count is guaranteed to be 1 at this point, and we required
416 // the `Rc<T>` itself to be `mut`, so we're returning the only possible
417 // reference to the inner value.
418 let inner
= unsafe { &mut **this._ptr }
;
423 #[stable(feature = "rust1", since = "1.0.0")]
424 impl<T
: ?Sized
> Deref
for Rc
<T
> {
428 fn deref(&self) -> &T
{
433 #[stable(feature = "rust1", since = "1.0.0")]
434 impl<T
: ?Sized
> Drop
for Rc
<T
> {
435 /// Drops the `Rc<T>`.
437 /// This will decrement the strong reference count. If the strong reference
438 /// count becomes zero and the only other references are `Weak<T>` ones,
439 /// `drop`s the inner value.
447 /// let five = Rc::new(5);
451 /// drop(five); // explicit drop
454 /// let five = Rc::new(5);
458 /// } // implicit drop
460 #[unsafe_destructor_blind_to_params]
463 let ptr
= *self._ptr
;
464 if !(*(&ptr
as *const _
as *const *const ())).is_null() &&
465 ptr
as *const () as usize != mem
::POST_DROP_USIZE
{
467 if self.strong() == 0 {
468 // destroy the contained object
469 ptr
::drop_in_place(&mut (*ptr
).value
);
471 // remove the implicit "strong weak" pointer now that we've
472 // destroyed the contents.
475 if self.weak() == 0 {
476 deallocate(ptr
as *mut u8, size_of_val(&*ptr
), align_of_val(&*ptr
))
484 #[stable(feature = "rust1", since = "1.0.0")]
485 impl<T
: ?Sized
> Clone
for Rc
<T
> {
486 /// Makes a clone of the `Rc<T>`.
488 /// When you clone an `Rc<T>`, it will create another pointer to the data and
489 /// increase the strong reference counter.
496 /// let five = Rc::new(5);
501 fn clone(&self) -> Rc
<T
> {
503 Rc { _ptr: self._ptr }
507 #[stable(feature = "rust1", since = "1.0.0")]
508 impl<T
: Default
> Default
for Rc
<T
> {
509 /// Creates a new `Rc<T>`, with the `Default` value for `T`.
516 /// let x: Rc<i32> = Default::default();
519 fn default() -> Rc
<T
> {
520 Rc
::new(Default
::default())
524 #[stable(feature = "rust1", since = "1.0.0")]
525 impl<T
: ?Sized
+ PartialEq
> PartialEq
for Rc
<T
> {
526 /// Equality for two `Rc<T>`s.
528 /// Two `Rc<T>`s are equal if their inner value are equal.
535 /// let five = Rc::new(5);
537 /// five == Rc::new(5);
540 fn eq(&self, other
: &Rc
<T
>) -> bool
{
544 /// Inequality for two `Rc<T>`s.
546 /// Two `Rc<T>`s are unequal if their inner value are unequal.
553 /// let five = Rc::new(5);
555 /// five != Rc::new(5);
558 fn ne(&self, other
: &Rc
<T
>) -> bool
{
563 #[stable(feature = "rust1", since = "1.0.0")]
564 impl<T
: ?Sized
+ Eq
> Eq
for Rc
<T
> {}
566 #[stable(feature = "rust1", since = "1.0.0")]
567 impl<T
: ?Sized
+ PartialOrd
> PartialOrd
for Rc
<T
> {
568 /// Partial comparison for two `Rc<T>`s.
570 /// The two are compared by calling `partial_cmp()` on their inner values.
577 /// let five = Rc::new(5);
579 /// five.partial_cmp(&Rc::new(5));
582 fn partial_cmp(&self, other
: &Rc
<T
>) -> Option
<Ordering
> {
583 (**self).partial_cmp(&**other
)
586 /// Less-than comparison for two `Rc<T>`s.
588 /// The two are compared by calling `<` on their inner values.
595 /// let five = Rc::new(5);
597 /// five < Rc::new(5);
600 fn lt(&self, other
: &Rc
<T
>) -> bool
{
604 /// 'Less-than or equal to' comparison for two `Rc<T>`s.
606 /// The two are compared by calling `<=` on their inner values.
613 /// let five = Rc::new(5);
615 /// five <= Rc::new(5);
618 fn le(&self, other
: &Rc
<T
>) -> bool
{
622 /// Greater-than comparison for two `Rc<T>`s.
624 /// The two are compared by calling `>` on their inner values.
631 /// let five = Rc::new(5);
633 /// five > Rc::new(5);
636 fn gt(&self, other
: &Rc
<T
>) -> bool
{
640 /// 'Greater-than or equal to' comparison for two `Rc<T>`s.
642 /// The two are compared by calling `>=` on their inner values.
649 /// let five = Rc::new(5);
651 /// five >= Rc::new(5);
654 fn ge(&self, other
: &Rc
<T
>) -> bool
{
659 #[stable(feature = "rust1", since = "1.0.0")]
660 impl<T
: ?Sized
+ Ord
> Ord
for Rc
<T
> {
661 /// Comparison for two `Rc<T>`s.
663 /// The two are compared by calling `cmp()` on their inner values.
670 /// let five = Rc::new(5);
672 /// five.partial_cmp(&Rc::new(5));
675 fn cmp(&self, other
: &Rc
<T
>) -> Ordering
{
676 (**self).cmp(&**other
)
680 #[stable(feature = "rust1", since = "1.0.0")]
681 impl<T
: ?Sized
+ Hash
> Hash
for Rc
<T
> {
682 fn hash
<H
: Hasher
>(&self, state
: &mut H
) {
683 (**self).hash(state
);
687 #[stable(feature = "rust1", since = "1.0.0")]
688 impl<T
: ?Sized
+ fmt
::Display
> fmt
::Display
for Rc
<T
> {
689 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
690 fmt
::Display
::fmt(&**self, f
)
694 #[stable(feature = "rust1", since = "1.0.0")]
695 impl<T
: ?Sized
+ fmt
::Debug
> fmt
::Debug
for Rc
<T
> {
696 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
697 fmt
::Debug
::fmt(&**self, f
)
701 #[stable(feature = "rust1", since = "1.0.0")]
702 impl<T
> fmt
::Pointer
for Rc
<T
> {
703 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
704 fmt
::Pointer
::fmt(&*self._ptr
, f
)
708 #[stable(feature = "from_for_ptrs", since = "1.6.0")]
709 impl<T
> From
<T
> for Rc
<T
> {
710 fn from(t
: T
) -> Self {
715 /// A weak version of `Rc<T>`.
717 /// Weak references do not count when determining if the inner value should be
720 /// See the [module level documentation](./index.html) for more.
721 #[unsafe_no_drop_flag]
722 #[stable(feature = "rc_weak", since = "1.4.0")]
723 pub struct Weak
<T
: ?Sized
> {
724 // FIXME #12808: strange names to try to avoid interfering with
725 // field accesses of the contained type via Deref
726 _ptr
: Shared
<RcBox
<T
>>,
729 #[stable(feature = "rust1", since = "1.0.0")]
730 impl<T
: ?Sized
> !marker
::Send
for Weak
<T
> {}
731 #[stable(feature = "rust1", since = "1.0.0")]
732 impl<T
: ?Sized
> !marker
::Sync
for Weak
<T
> {}
734 // remove cfg after new snapshot
736 #[unstable(feature = "coerce_unsized", issue = "27732")]
737 impl<T
: ?Sized
+ Unsize
<U
>, U
: ?Sized
> CoerceUnsized
<Weak
<U
>> for Weak
<T
> {}
739 impl<T
: ?Sized
> Weak
<T
> {
740 /// Upgrades a weak reference to a strong reference.
742 /// Upgrades the `Weak<T>` reference to an `Rc<T>`, if possible.
744 /// Returns `None` if there were no strong references and the data was
752 /// let five = Rc::new(5);
754 /// let weak_five = Rc::downgrade(&five);
756 /// let strong_five: Option<Rc<_>> = weak_five.upgrade();
758 #[stable(feature = "rc_weak", since = "1.4.0")]
759 pub fn upgrade(&self) -> Option
<Rc
<T
>> {
760 if self.strong() == 0 {
764 Some(Rc { _ptr: self._ptr }
)
769 #[stable(feature = "rust1", since = "1.0.0")]
770 impl<T
: ?Sized
> Drop
for Weak
<T
> {
771 /// Drops the `Weak<T>`.
773 /// This will decrement the weak reference count.
781 /// let five = Rc::new(5);
782 /// let weak_five = Rc::downgrade(&five);
786 /// drop(weak_five); // explicit drop
789 /// let five = Rc::new(5);
790 /// let weak_five = Rc::downgrade(&five);
794 /// } // implicit drop
798 let ptr
= *self._ptr
;
799 if !(*(&ptr
as *const _
as *const *const ())).is_null() &&
800 ptr
as *const () as usize != mem
::POST_DROP_USIZE
{
802 // the weak count starts at 1, and will only go to zero if all
803 // the strong pointers have disappeared.
804 if self.weak() == 0 {
805 deallocate(ptr
as *mut u8, size_of_val(&*ptr
), align_of_val(&*ptr
))
812 #[stable(feature = "rc_weak", since = "1.4.0")]
813 impl<T
: ?Sized
> Clone
for Weak
<T
> {
814 /// Makes a clone of the `Weak<T>`.
816 /// This increases the weak reference count.
823 /// let weak_five = Rc::downgrade(&Rc::new(5));
825 /// weak_five.clone();
828 fn clone(&self) -> Weak
<T
> {
830 Weak { _ptr: self._ptr }
834 #[stable(feature = "rust1", since = "1.0.0")]
835 impl<T
: ?Sized
+ fmt
::Debug
> fmt
::Debug
for Weak
<T
> {
836 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
841 // NOTE: We checked_add here to deal with mem::forget safety. In particular
842 // if you mem::forget Rcs (or Weaks), the ref-count can overflow, and then
843 // you can free the allocation while outstanding Rcs (or Weaks) exist.
844 // We abort because this is such a degenerate scenario that we don't care about
845 // what happens -- no real program should ever experience this.
847 // This should have negligible overhead since you don't actually need to
848 // clone these much in Rust thanks to ownership and move-semantics.
851 trait RcBoxPtr
<T
: ?Sized
> {
852 fn inner(&self) -> &RcBox
<T
>;
855 fn strong(&self) -> usize {
856 self.inner().strong
.get()
860 fn inc_strong(&self) {
861 self.inner().strong
.set(self.strong().checked_add(1).unwrap_or_else(|| unsafe { abort() }
));
865 fn dec_strong(&self) {
866 self.inner().strong
.set(self.strong() - 1);
870 fn weak(&self) -> usize {
871 self.inner().weak
.get()
876 self.inner().weak
.set(self.weak().checked_add(1).unwrap_or_else(|| unsafe { abort() }
));
881 self.inner().weak
.set(self.weak() - 1);
885 impl<T
: ?Sized
> RcBoxPtr
<T
> for Rc
<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());
899 impl<T
: ?Sized
> RcBoxPtr
<T
> for Weak
<T
> {
901 fn inner(&self) -> &RcBox
<T
> {
903 // Safe to assume this here, as if it weren't true, we'd be breaking
904 // the contract anyway.
905 // This allows the null check to be elided in the destructor if we
906 // manipulated the reference count in the same function.
907 assume(!(*(&self._ptr
as *const _
as *const *const ())).is_null());
915 use super::{Rc, Weak}
;
917 use std
::cell
::RefCell
;
918 use std
::option
::Option
;
919 use std
::option
::Option
::{Some, None}
;
920 use std
::result
::Result
::{Err, Ok}
;
922 use std
::clone
::Clone
;
923 use std
::convert
::From
;
927 let x
= Rc
::new(RefCell
::new(5));
929 *x
.borrow_mut() = 20;
930 assert_eq
!(*y
.borrow(), 20);
940 fn test_simple_clone() {
948 fn test_destructor() {
949 let x
: Rc
<Box
<_
>> = Rc
::new(box 5);
956 let y
= Rc
::downgrade(&x
);
957 assert
!(y
.upgrade().is_some());
963 let y
= Rc
::downgrade(&x
);
965 assert
!(y
.upgrade().is_none());
969 fn weak_self_cyclic() {
971 x
: RefCell
<Option
<Weak
<Cycle
>>>,
974 let a
= Rc
::new(Cycle { x: RefCell::new(None) }
);
975 let b
= Rc
::downgrade(&a
.clone());
976 *a
.x
.borrow_mut() = Some(b
);
978 // hopefully we don't double-free (or leak)...
984 assert
!(Rc
::is_unique(&x
));
986 assert
!(!Rc
::is_unique(&x
));
988 assert
!(Rc
::is_unique(&x
));
989 let w
= Rc
::downgrade(&x
);
990 assert
!(!Rc
::is_unique(&x
));
992 assert
!(Rc
::is_unique(&x
));
996 fn test_strong_count() {
997 let a
= Rc
::new(0u32);
998 assert
!(Rc
::strong_count(&a
) == 1);
999 let w
= Rc
::downgrade(&a
);
1000 assert
!(Rc
::strong_count(&a
) == 1);
1001 let b
= w
.upgrade().expect("upgrade of live rc failed");
1002 assert
!(Rc
::strong_count(&b
) == 2);
1003 assert
!(Rc
::strong_count(&a
) == 2);
1006 assert
!(Rc
::strong_count(&b
) == 1);
1008 assert
!(Rc
::strong_count(&b
) == 2);
1009 assert
!(Rc
::strong_count(&c
) == 2);
1013 fn test_weak_count() {
1014 let a
= Rc
::new(0u32);
1015 assert
!(Rc
::strong_count(&a
) == 1);
1016 assert
!(Rc
::weak_count(&a
) == 0);
1017 let w
= Rc
::downgrade(&a
);
1018 assert
!(Rc
::strong_count(&a
) == 1);
1019 assert
!(Rc
::weak_count(&a
) == 1);
1021 assert
!(Rc
::strong_count(&a
) == 1);
1022 assert
!(Rc
::weak_count(&a
) == 0);
1024 assert
!(Rc
::strong_count(&a
) == 2);
1025 assert
!(Rc
::weak_count(&a
) == 0);
1032 assert_eq
!(Rc
::try_unwrap(x
), Ok(3));
1035 assert_eq
!(Rc
::try_unwrap(x
), Err(Rc
::new(4)));
1037 let _w
= Rc
::downgrade(&x
);
1038 assert_eq
!(Rc
::try_unwrap(x
), Ok(5));
1043 let mut x
= Rc
::new(3);
1044 *Rc
::get_mut(&mut x
).unwrap() = 4;
1047 assert
!(Rc
::get_mut(&mut x
).is_none());
1049 assert
!(Rc
::get_mut(&mut x
).is_some());
1050 let _w
= Rc
::downgrade(&x
);
1051 assert
!(Rc
::get_mut(&mut x
).is_none());
1055 fn test_cowrc_clone_make_unique() {
1056 let mut cow0
= Rc
::new(75);
1057 let mut cow1
= cow0
.clone();
1058 let mut cow2
= cow1
.clone();
1060 assert
!(75 == *Rc
::make_mut(&mut cow0
));
1061 assert
!(75 == *Rc
::make_mut(&mut cow1
));
1062 assert
!(75 == *Rc
::make_mut(&mut cow2
));
1064 *Rc
::make_mut(&mut cow0
) += 1;
1065 *Rc
::make_mut(&mut cow1
) += 2;
1066 *Rc
::make_mut(&mut cow2
) += 3;
1068 assert
!(76 == *cow0
);
1069 assert
!(77 == *cow1
);
1070 assert
!(78 == *cow2
);
1072 // none should point to the same backing memory
1073 assert
!(*cow0
!= *cow1
);
1074 assert
!(*cow0
!= *cow2
);
1075 assert
!(*cow1
!= *cow2
);
1079 fn test_cowrc_clone_unique2() {
1080 let mut cow0
= Rc
::new(75);
1081 let cow1
= cow0
.clone();
1082 let cow2
= cow1
.clone();
1084 assert
!(75 == *cow0
);
1085 assert
!(75 == *cow1
);
1086 assert
!(75 == *cow2
);
1088 *Rc
::make_mut(&mut cow0
) += 1;
1090 assert
!(76 == *cow0
);
1091 assert
!(75 == *cow1
);
1092 assert
!(75 == *cow2
);
1094 // cow1 and cow2 should share the same contents
1095 // cow0 should have a unique reference
1096 assert
!(*cow0
!= *cow1
);
1097 assert
!(*cow0
!= *cow2
);
1098 assert
!(*cow1
== *cow2
);
1102 fn test_cowrc_clone_weak() {
1103 let mut cow0
= Rc
::new(75);
1104 let cow1_weak
= Rc
::downgrade(&cow0
);
1106 assert
!(75 == *cow0
);
1107 assert
!(75 == *cow1_weak
.upgrade().unwrap());
1109 *Rc
::make_mut(&mut cow0
) += 1;
1111 assert
!(76 == *cow0
);
1112 assert
!(cow1_weak
.upgrade().is_none());
1117 let foo
= Rc
::new(75);
1118 assert_eq
!(format
!("{:?}", foo
), "75");
1123 let foo
: Rc
<[i32]> = Rc
::new([1, 2, 3]);
1124 assert_eq
!(foo
, foo
.clone());
1128 fn test_from_owned() {
1130 let foo_rc
= Rc
::from(foo
);
1131 assert
!(123 == *foo_rc
);
1135 #[stable(feature = "rust1", since = "1.0.0")]
1136 impl<T
: ?Sized
> borrow
::Borrow
<T
> for Rc
<T
> {
1137 fn borrow(&self) -> &T
{
1142 #[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
1143 impl<T
: ?Sized
> AsRef
<T
> for Rc
<T
> {
1144 fn as_ref(&self) -> &T
{