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 //! Unsynchronized reference-counted boxes (the `Rc<T>` type) which are usable
14 //! only within a single thread.
16 //! The `Rc<T>` type provides shared ownership of an immutable value.
17 //! Destruction is deterministic, and will occur as soon as the last owner is
18 //! gone. It is marked as non-sendable because it avoids the overhead of atomic
19 //! reference counting.
21 //! The `downgrade` method can be used to create a non-owning `Weak<T>` pointer
22 //! to the box. A `Weak<T>` pointer can be upgraded to an `Rc<T>` pointer, but
23 //! will return `None` if the value has already been dropped.
25 //! For example, a tree with parent pointers can be represented by putting the
26 //! nodes behind strong `Rc<T>` pointers, and then storing the parent pointers
27 //! as `Weak<T>` pointers.
31 //! Consider a scenario where a set of `Gadget`s are owned by a given `Owner`.
32 //! We want to have our `Gadget`s point to their `Owner`. We can't do this with
33 //! unique ownership, because more than one gadget may belong to the same
34 //! `Owner`. `Rc<T>` allows us to share an `Owner` between multiple `Gadget`s,
35 //! and have the `Owner` remain allocated as long as any `Gadget` points at it.
42 //! // ...other fields
48 //! // ...other fields
52 //! // Create a reference counted Owner.
53 //! let gadget_owner : Rc<Owner> = Rc::new(
54 //! Owner { name: String::from("Gadget Man") }
57 //! // Create Gadgets belonging to gadget_owner. To increment the reference
58 //! // count we clone the `Rc<T>` object.
59 //! let gadget1 = Gadget { id: 1, owner: gadget_owner.clone() };
60 //! let gadget2 = Gadget { id: 2, owner: gadget_owner.clone() };
62 //! drop(gadget_owner);
64 //! // Despite dropping gadget_owner, we're still able to print out the name
65 //! // of the Owner of the Gadgets. This is because we've only dropped the
66 //! // reference count object, not the Owner it wraps. As long as there are
67 //! // other `Rc<T>` objects pointing at the same Owner, it will remain
68 //! // allocated. Notice that the `Rc<T>` wrapper around Gadget.owner gets
69 //! // automatically dereferenced for us.
70 //! println!("Gadget {} owned by {}", gadget1.id, gadget1.owner.name);
71 //! println!("Gadget {} owned by {}", gadget2.id, gadget2.owner.name);
73 //! // At the end of the method, gadget1 and gadget2 get destroyed, and with
74 //! // them the last counted references to our Owner. Gadget Man now gets
75 //! // destroyed as well.
79 //! If our requirements change, and we also need to be able to traverse from
80 //! Owner → Gadget, we will run into problems: an `Rc<T>` pointer from Owner
81 //! → Gadget introduces a cycle between the objects. This means that their
82 //! reference counts can never reach 0, and the objects will remain allocated: a
83 //! memory leak. In order to get around this, we can use `Weak<T>` pointers.
84 //! These pointers don't contribute to the total count.
86 //! Rust actually makes it somewhat difficult to produce this loop in the first
87 //! place: in order to end up with two objects that point at each other, one of
88 //! them needs to be mutable. This is problematic because `Rc<T>` enforces
89 //! memory safety by only giving out shared references to the object it wraps,
90 //! and these don't allow direct mutation. We need to wrap the part of the
91 //! object we wish to mutate in a `RefCell`, which provides *interior
92 //! mutability*: a method to achieve mutability through a shared reference.
93 //! `RefCell` enforces Rust's borrowing rules at runtime. Read the `Cell`
94 //! documentation for more details on interior mutability.
98 //! use std::rc::Weak;
99 //! use std::cell::RefCell;
103 //! gadgets: RefCell<Vec<Weak<Gadget>>>,
104 //! // ...other fields
109 //! owner: Rc<Owner>,
110 //! // ...other fields
114 //! // Create a reference counted Owner. Note the fact that we've put the
115 //! // Owner's vector of Gadgets inside a RefCell so that we can mutate it
116 //! // through a shared reference.
117 //! let gadget_owner : Rc<Owner> = Rc::new(
119 //! name: "Gadget Man".to_string(),
120 //! gadgets: RefCell::new(Vec::new()),
124 //! // Create Gadgets belonging to gadget_owner as before.
125 //! let gadget1 = Rc::new(Gadget{id: 1, owner: gadget_owner.clone()});
126 //! let gadget2 = Rc::new(Gadget{id: 2, owner: gadget_owner.clone()});
128 //! // Add the Gadgets to their Owner. To do this we mutably borrow from
129 //! // the RefCell holding the Owner's Gadgets.
130 //! gadget_owner.gadgets.borrow_mut().push(Rc::downgrade(&gadget1));
131 //! gadget_owner.gadgets.borrow_mut().push(Rc::downgrade(&gadget2));
133 //! // Iterate over our Gadgets, printing their details out
134 //! for gadget_opt in gadget_owner.gadgets.borrow().iter() {
136 //! // gadget_opt is a Weak<Gadget>. Since weak pointers can't guarantee
137 //! // that their object is still allocated, we need to call upgrade()
138 //! // on them to turn them into a strong reference. This returns an
139 //! // Option, which contains a reference to our object if it still
141 //! let gadget = gadget_opt.upgrade().unwrap();
142 //! println!("Gadget {} owned by {}", gadget.id, gadget.owner.name);
145 //! // At the end of the method, gadget_owner, gadget1 and gadget2 get
146 //! // destroyed. There are now no strong (`Rc<T>`) references to the gadgets.
147 //! // Once they get destroyed, the Gadgets get destroyed. This zeroes the
148 //! // reference count on Gadget Man, they get destroyed as well.
152 #![stable(feature = "rust1", since = "1.0.0")]
160 use core
::cell
::Cell
;
161 use core
::cmp
::Ordering
;
163 use core
::hash
::{Hash, Hasher}
;
164 use core
::intrinsics
::{abort, assume}
;
166 use core
::marker
::Unsize
;
167 use core
::mem
::{self, align_of_val, forget, size_of_val, uninitialized}
;
168 use core
::ops
::Deref
;
169 use core
::ops
::CoerceUnsized
;
170 use core
::ptr
::{self, Shared}
;
171 use core
::convert
::From
;
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 ptr
: Shared
<RcBox
<T
>>,
191 #[stable(feature = "rust1", since = "1.0.0")]
192 impl<T
: ?Sized
> !marker
::Send
for Rc
<T
> {}
193 #[stable(feature = "rust1", since = "1.0.0")]
194 impl<T
: ?Sized
> !marker
::Sync
for Rc
<T
> {}
196 #[unstable(feature = "coerce_unsized", issue = "27732")]
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 exactly one strong reference.
228 /// Otherwise, an `Err` is returned with the same `Rc<T>`.
230 /// This will succeed even if there are outstanding weak references.
237 /// let x = Rc::new(3);
238 /// assert_eq!(Rc::try_unwrap(x), Ok(3));
240 /// let x = Rc::new(4);
241 /// let _y = x.clone();
242 /// assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4)));
245 #[stable(feature = "rc_unique", since = "1.4.0")]
246 pub fn try_unwrap(this
: Self) -> Result
<T
, Self> {
247 if Rc
::would_unwrap(&this
) {
249 let val
= ptr
::read(&*this
); // copy the contained object
251 // Indicate to Weaks that they can't be promoted by decrememting
252 // the strong count, and then remove the implicit "strong weak"
253 // pointer while also handling drop logic by just crafting a
256 let _weak
= Weak { ptr: this.ptr }
;
265 /// Checks if `Rc::try_unwrap` would return `Ok`.
266 #[unstable(feature = "rc_would_unwrap",
267 reason
= "just added for niche usecase",
269 pub fn would_unwrap(this
: &Self) -> bool
{
270 Rc
::strong_count(&this
) == 1
274 impl<T
: ?Sized
> Rc
<T
> {
275 /// Creates a new `Weak<T>` reference from this value.
282 /// let five = Rc::new(5);
284 /// let weak_five = Rc::downgrade(&five);
286 #[stable(feature = "rc_weak", since = "1.4.0")]
287 pub fn downgrade(this
: &Self) -> Weak
<T
> {
289 Weak { ptr: this.ptr }
292 /// Get the number of weak references to this value.
294 #[unstable(feature = "rc_counts", reason = "not clearly useful",
296 pub fn weak_count(this
: &Self) -> usize {
300 /// Get the number of strong references to this value.
302 #[unstable(feature = "rc_counts", reason = "not clearly useful",
304 pub fn strong_count(this
: &Self) -> usize {
308 /// Returns true if there are no other `Rc` or `Weak<T>` values that share
309 /// the same inner value.
314 /// #![feature(rc_counts)]
318 /// let five = Rc::new(5);
320 /// assert!(Rc::is_unique(&five));
323 #[unstable(feature = "rc_counts", reason = "uniqueness has unclear meaning",
325 pub fn is_unique(this
: &Self) -> bool
{
326 Rc
::weak_count(this
) == 0 && Rc
::strong_count(this
) == 1
329 /// Returns a mutable reference to the contained value if the `Rc<T>` has
330 /// one strong reference and no weak references.
332 /// Returns `None` if the `Rc<T>` is not unique.
339 /// let mut x = Rc::new(3);
340 /// *Rc::get_mut(&mut x).unwrap() = 4;
341 /// assert_eq!(*x, 4);
343 /// let _y = x.clone();
344 /// assert!(Rc::get_mut(&mut x).is_none());
347 #[stable(feature = "rc_unique", since = "1.4.0")]
348 pub fn get_mut(this
: &mut Self) -> Option
<&mut T
> {
349 if Rc
::is_unique(this
) {
350 let inner
= unsafe { &mut **this.ptr }
;
351 Some(&mut inner
.value
)
358 impl<T
: Clone
> Rc
<T
> {
359 /// Make a mutable reference into the given `Rc<T>` by cloning the inner
360 /// data if the `Rc<T>` doesn't have one strong reference and no weak
363 /// This is also referred to as a copy-on-write.
370 /// let mut data = Rc::new(5);
372 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
373 /// let mut other_data = data.clone(); // Won't clone inner data
374 /// *Rc::make_mut(&mut data) += 1; // Clones inner data
375 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
376 /// *Rc::make_mut(&mut other_data) *= 2; // Won't clone anything
378 /// // Note: data and other_data now point to different numbers
379 /// assert_eq!(*data, 8);
380 /// assert_eq!(*other_data, 12);
384 #[stable(feature = "rc_unique", since = "1.4.0")]
385 pub fn make_mut(this
: &mut Self) -> &mut T
{
386 if Rc
::strong_count(this
) != 1 {
387 // Gotta clone the data, there are other Rcs
388 *this
= Rc
::new((**this
).clone())
389 } else if Rc
::weak_count(this
) != 0 {
390 // Can just steal the data, all that's left is Weaks
392 let mut swap
= Rc
::new(ptr
::read(&(**this
.ptr
).value
));
393 mem
::swap(this
, &mut swap
);
395 // Remove implicit strong-weak ref (no need to craft a fake
396 // Weak here -- we know other Weaks can clean up for us)
401 // This unsafety is ok because we're guaranteed that the pointer
402 // returned is the *only* pointer that will ever be returned to T. Our
403 // reference count is guaranteed to be 1 at this point, and we required
404 // the `Rc<T>` itself to be `mut`, so we're returning the only possible
405 // reference to the inner value.
406 let inner
= unsafe { &mut **this.ptr }
;
411 #[stable(feature = "rust1", since = "1.0.0")]
412 impl<T
: ?Sized
> Deref
for Rc
<T
> {
416 fn deref(&self) -> &T
{
421 #[stable(feature = "rust1", since = "1.0.0")]
422 impl<T
: ?Sized
> Drop
for Rc
<T
> {
423 /// Drops the `Rc<T>`.
425 /// This will decrement the strong reference count. If the strong reference
426 /// count becomes zero and the only other references are `Weak<T>` ones,
427 /// `drop`s the inner value.
435 /// let five = Rc::new(5);
439 /// drop(five); // explicit drop
442 /// let five = Rc::new(5);
446 /// } // implicit drop
448 #[unsafe_destructor_blind_to_params]
452 let thin
= ptr
as *const ();
454 if thin
as usize != mem
::POST_DROP_USIZE
{
456 if self.strong() == 0 {
457 // destroy the contained object
458 ptr
::drop_in_place(&mut (*ptr
).value
);
460 // remove the implicit "strong weak" pointer now that we've
461 // destroyed the contents.
464 if self.weak() == 0 {
465 deallocate(ptr
as *mut u8, size_of_val(&*ptr
), align_of_val(&*ptr
))
473 #[stable(feature = "rust1", since = "1.0.0")]
474 impl<T
: ?Sized
> Clone
for Rc
<T
> {
475 /// Makes a clone of the `Rc<T>`.
477 /// When you clone an `Rc<T>`, it will create another pointer to the data and
478 /// increase the strong reference counter.
485 /// let five = Rc::new(5);
490 fn clone(&self) -> Rc
<T
> {
496 #[stable(feature = "rust1", since = "1.0.0")]
497 impl<T
: Default
> Default
for Rc
<T
> {
498 /// Creates a new `Rc<T>`, with the `Default` value for `T`.
505 /// let x: Rc<i32> = Default::default();
508 fn default() -> Rc
<T
> {
509 Rc
::new(Default
::default())
513 #[stable(feature = "rust1", since = "1.0.0")]
514 impl<T
: ?Sized
+ PartialEq
> PartialEq
for Rc
<T
> {
515 /// Equality for two `Rc<T>`s.
517 /// Two `Rc<T>`s are equal if their inner value are equal.
524 /// let five = Rc::new(5);
526 /// five == Rc::new(5);
529 fn eq(&self, other
: &Rc
<T
>) -> bool
{
533 /// Inequality for two `Rc<T>`s.
535 /// Two `Rc<T>`s are unequal if their inner value are unequal.
542 /// let five = Rc::new(5);
544 /// five != Rc::new(5);
547 fn ne(&self, other
: &Rc
<T
>) -> bool
{
552 #[stable(feature = "rust1", since = "1.0.0")]
553 impl<T
: ?Sized
+ Eq
> Eq
for Rc
<T
> {}
555 #[stable(feature = "rust1", since = "1.0.0")]
556 impl<T
: ?Sized
+ PartialOrd
> PartialOrd
for Rc
<T
> {
557 /// Partial comparison for two `Rc<T>`s.
559 /// The two are compared by calling `partial_cmp()` on their inner values.
566 /// let five = Rc::new(5);
568 /// five.partial_cmp(&Rc::new(5));
571 fn partial_cmp(&self, other
: &Rc
<T
>) -> Option
<Ordering
> {
572 (**self).partial_cmp(&**other
)
575 /// Less-than comparison for two `Rc<T>`s.
577 /// The two are compared by calling `<` on their inner values.
584 /// let five = Rc::new(5);
586 /// five < Rc::new(5);
589 fn lt(&self, other
: &Rc
<T
>) -> bool
{
593 /// 'Less-than or equal to' comparison for two `Rc<T>`s.
595 /// The two are compared by calling `<=` on their inner values.
602 /// let five = Rc::new(5);
604 /// five <= Rc::new(5);
607 fn le(&self, other
: &Rc
<T
>) -> bool
{
611 /// Greater-than comparison for two `Rc<T>`s.
613 /// The two are compared by calling `>` on their inner values.
620 /// let five = Rc::new(5);
622 /// five > Rc::new(5);
625 fn gt(&self, other
: &Rc
<T
>) -> bool
{
629 /// 'Greater-than or equal to' comparison for two `Rc<T>`s.
631 /// The two are compared by calling `>=` on their inner values.
638 /// let five = Rc::new(5);
640 /// five >= Rc::new(5);
643 fn ge(&self, other
: &Rc
<T
>) -> bool
{
648 #[stable(feature = "rust1", since = "1.0.0")]
649 impl<T
: ?Sized
+ Ord
> Ord
for Rc
<T
> {
650 /// Comparison for two `Rc<T>`s.
652 /// The two are compared by calling `cmp()` on their inner values.
659 /// let five = Rc::new(5);
661 /// five.partial_cmp(&Rc::new(5));
664 fn cmp(&self, other
: &Rc
<T
>) -> Ordering
{
665 (**self).cmp(&**other
)
669 #[stable(feature = "rust1", since = "1.0.0")]
670 impl<T
: ?Sized
+ Hash
> Hash
for Rc
<T
> {
671 fn hash
<H
: Hasher
>(&self, state
: &mut H
) {
672 (**self).hash(state
);
676 #[stable(feature = "rust1", since = "1.0.0")]
677 impl<T
: ?Sized
+ fmt
::Display
> fmt
::Display
for Rc
<T
> {
678 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
679 fmt
::Display
::fmt(&**self, f
)
683 #[stable(feature = "rust1", since = "1.0.0")]
684 impl<T
: ?Sized
+ fmt
::Debug
> fmt
::Debug
for Rc
<T
> {
685 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
686 fmt
::Debug
::fmt(&**self, f
)
690 #[stable(feature = "rust1", since = "1.0.0")]
691 impl<T
: ?Sized
> fmt
::Pointer
for Rc
<T
> {
692 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
693 fmt
::Pointer
::fmt(&*self.ptr
, f
)
697 #[stable(feature = "from_for_ptrs", since = "1.6.0")]
698 impl<T
> From
<T
> for Rc
<T
> {
699 fn from(t
: T
) -> Self {
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 ptr
: Shared
<RcBox
<T
>>,
716 #[stable(feature = "rc_weak", since = "1.4.0")]
717 impl<T
: ?Sized
> !marker
::Send
for Weak
<T
> {}
718 #[stable(feature = "rc_weak", since = "1.4.0")]
719 impl<T
: ?Sized
> !marker
::Sync
for Weak
<T
> {}
721 #[unstable(feature = "coerce_unsized", issue = "27732")]
722 impl<T
: ?Sized
+ Unsize
<U
>, U
: ?Sized
> CoerceUnsized
<Weak
<U
>> for Weak
<T
> {}
725 /// Constructs a new `Weak<T>` without an accompanying instance of T.
727 /// This allocates memory for T, but does not initialize it. Calling
728 /// Weak<T>::upgrade() on the return value always gives None.
733 /// use std::rc::Weak;
735 /// let empty: Weak<i64> = Weak::new();
737 #[stable(feature = "downgraded_weak", since = "1.10.0")]
738 pub fn new() -> Weak
<T
> {
741 ptr
: Shared
::new(Box
::into_raw(box RcBox
{
742 strong
: Cell
::new(0),
744 value
: uninitialized(),
751 impl<T
: ?Sized
> Weak
<T
> {
752 /// Upgrades a weak reference to a strong reference.
754 /// Upgrades the `Weak<T>` reference to an `Rc<T>`, if possible.
756 /// Returns `None` if there were no strong references and the data was
764 /// let five = Rc::new(5);
766 /// let weak_five = Rc::downgrade(&five);
768 /// let strong_five: Option<Rc<_>> = weak_five.upgrade();
770 #[stable(feature = "rc_weak", since = "1.4.0")]
771 pub fn upgrade(&self) -> Option
<Rc
<T
>> {
772 if self.strong() == 0 {
776 Some(Rc { ptr: self.ptr }
)
781 #[stable(feature = "rc_weak", since = "1.4.0")]
782 impl<T
: ?Sized
> Drop
for Weak
<T
> {
783 /// Drops the `Weak<T>`.
785 /// This will decrement the weak reference count.
793 /// let five = Rc::new(5);
794 /// let weak_five = Rc::downgrade(&five);
798 /// drop(weak_five); // explicit drop
801 /// let five = Rc::new(5);
802 /// let weak_five = Rc::downgrade(&five);
806 /// } // implicit drop
811 let thin
= ptr
as *const ();
813 if thin
as usize != mem
::POST_DROP_USIZE
{
815 // the weak count starts at 1, and will only go to zero if all
816 // the strong pointers have disappeared.
817 if self.weak() == 0 {
818 deallocate(ptr
as *mut u8, size_of_val(&*ptr
), align_of_val(&*ptr
))
825 #[stable(feature = "rc_weak", since = "1.4.0")]
826 impl<T
: ?Sized
> Clone
for Weak
<T
> {
827 /// Makes a clone of the `Weak<T>`.
829 /// This increases the weak reference count.
836 /// let weak_five = Rc::downgrade(&Rc::new(5));
838 /// weak_five.clone();
841 fn clone(&self) -> Weak
<T
> {
843 Weak { ptr: self.ptr }
847 #[stable(feature = "rc_weak", since = "1.4.0")]
848 impl<T
: ?Sized
+ fmt
::Debug
> fmt
::Debug
for Weak
<T
> {
849 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
854 #[stable(feature = "downgraded_weak", since = "1.10.0")]
855 impl<T
> Default
for Weak
<T
> {
856 fn default() -> Weak
<T
> {
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
::{None, Some}
;
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
{