1 //! Single-threaded reference-counting pointers. 'Rc' stands for 'Reference
4 //! The type [`Rc<T>`][`Rc`] provides shared ownership of a value of type `T`,
5 //! allocated in the heap. Invoking [`clone`][clone] on [`Rc`] produces a new
6 //! pointer to the same value in the heap. When the last [`Rc`] pointer to a
7 //! given value is destroyed, the pointed-to value is also destroyed.
9 //! Shared references in Rust disallow mutation by default, and [`Rc`]
10 //! is no exception: you cannot generally obtain a mutable reference to
11 //! something inside an [`Rc`]. If you need mutability, put a [`Cell`]
12 //! or [`RefCell`] inside the [`Rc`]; see [an example of mutability
13 //! inside an Rc][mutability].
15 //! [`Rc`] uses non-atomic reference counting. This means that overhead is very
16 //! low, but an [`Rc`] cannot be sent between threads, and consequently [`Rc`]
17 //! does not implement [`Send`][send]. As a result, the Rust compiler
18 //! will check *at compile time* that you are not sending [`Rc`]s between
19 //! threads. If you need multi-threaded, atomic reference counting, use
20 //! [`sync::Arc`][arc].
22 //! The [`downgrade`][downgrade] method can be used to create a non-owning
23 //! [`Weak`] pointer. A [`Weak`] pointer can be [`upgrade`][upgrade]d
24 //! to an [`Rc`], but this will return [`None`] if the value has
25 //! already been dropped.
27 //! A cycle between [`Rc`] pointers will never be deallocated. For this reason,
28 //! [`Weak`] is used to break cycles. For example, a tree could have strong
29 //! [`Rc`] pointers from parent nodes to children, and [`Weak`] pointers from
30 //! children back to their parents.
32 //! `Rc<T>` automatically dereferences to `T` (via the [`Deref`] trait),
33 //! so you can call `T`'s methods on a value of type [`Rc<T>`][`Rc`]. To avoid name
34 //! clashes with `T`'s methods, the methods of [`Rc<T>`][`Rc`] itself are associated
35 //! functions, called using function-like syntax:
39 //! let my_rc = Rc::new(());
41 //! Rc::downgrade(&my_rc);
44 //! [`Weak<T>`][`Weak`] does not auto-dereference to `T`, because the value may have
45 //! already been destroyed.
47 //! # Cloning references
49 //! Creating a new reference from an existing reference counted pointer is done using the
50 //! `Clone` trait implemented for [`Rc<T>`][`Rc`] and [`Weak<T>`][`Weak`].
54 //! let foo = Rc::new(vec![1.0, 2.0, 3.0]);
55 //! // The two syntaxes below are equivalent.
56 //! let a = foo.clone();
57 //! let b = Rc::clone(&foo);
58 //! // a and b both point to the same memory location as foo.
61 //! The `Rc::clone(&from)` syntax is the most idiomatic because it conveys more explicitly
62 //! the meaning of the code. In the example above, this syntax makes it easier to see that
63 //! this code is creating a new reference rather than copying the whole content of foo.
67 //! Consider a scenario where a set of `Gadget`s are owned by a given `Owner`.
68 //! We want to have our `Gadget`s point to their `Owner`. We can't do this with
69 //! unique ownership, because more than one gadget may belong to the same
70 //! `Owner`. [`Rc`] allows us to share an `Owner` between multiple `Gadget`s,
71 //! and have the `Owner` remain allocated as long as any `Gadget` points at it.
78 //! // ...other fields
84 //! // ...other fields
88 //! // Create a reference-counted `Owner`.
89 //! let gadget_owner: Rc<Owner> = Rc::new(
91 //! name: "Gadget Man".to_string(),
95 //! // Create `Gadget`s belonging to `gadget_owner`. Cloning the `Rc<Owner>`
96 //! // value gives us a new pointer to the same `Owner` value, incrementing
97 //! // the reference count in the process.
98 //! let gadget1 = Gadget {
100 //! owner: Rc::clone(&gadget_owner),
102 //! let gadget2 = Gadget {
104 //! owner: Rc::clone(&gadget_owner),
107 //! // Dispose of our local variable `gadget_owner`.
108 //! drop(gadget_owner);
110 //! // Despite dropping `gadget_owner`, we're still able to print out the name
111 //! // of the `Owner` of the `Gadget`s. This is because we've only dropped a
112 //! // single `Rc<Owner>`, not the `Owner` it points to. As long as there are
113 //! // other `Rc<Owner>` values pointing at the same `Owner`, it will remain
114 //! // allocated. The field projection `gadget1.owner.name` works because
115 //! // `Rc<Owner>` automatically dereferences to `Owner`.
116 //! println!("Gadget {} owned by {}", gadget1.id, gadget1.owner.name);
117 //! println!("Gadget {} owned by {}", gadget2.id, gadget2.owner.name);
119 //! // At the end of the function, `gadget1` and `gadget2` are destroyed, and
120 //! // with them the last counted references to our `Owner`. Gadget Man now
121 //! // gets destroyed as well.
125 //! If our requirements change, and we also need to be able to traverse from
126 //! `Owner` to `Gadget`, we will run into problems. An [`Rc`] pointer from `Owner`
127 //! to `Gadget` introduces a cycle between the values. This means that their
128 //! reference counts can never reach 0, and the values will remain allocated
129 //! forever: a memory leak. In order to get around this, we can use [`Weak`]
132 //! Rust actually makes it somewhat difficult to produce this loop in the first
133 //! place. In order to end up with two values that point at each other, one of
134 //! them needs to be mutable. This is difficult because [`Rc`] enforces
135 //! memory safety by only giving out shared references to the value it wraps,
136 //! and these don't allow direct mutation. We need to wrap the part of the
137 //! value we wish to mutate in a [`RefCell`], which provides *interior
138 //! mutability*: a method to achieve mutability through a shared reference.
139 //! [`RefCell`] enforces Rust's borrowing rules at runtime.
143 //! use std::rc::Weak;
144 //! use std::cell::RefCell;
148 //! gadgets: RefCell<Vec<Weak<Gadget>>>,
149 //! // ...other fields
154 //! owner: Rc<Owner>,
155 //! // ...other fields
159 //! // Create a reference-counted `Owner`. Note that we've put the `Owner`'s
160 //! // vector of `Gadget`s inside a `RefCell` so that we can mutate it through
161 //! // a shared reference.
162 //! let gadget_owner: Rc<Owner> = Rc::new(
164 //! name: "Gadget Man".to_string(),
165 //! gadgets: RefCell::new(vec![]),
169 //! // Create `Gadget`s belonging to `gadget_owner`, as before.
170 //! let gadget1 = Rc::new(
173 //! owner: Rc::clone(&gadget_owner),
176 //! let gadget2 = Rc::new(
179 //! owner: Rc::clone(&gadget_owner),
183 //! // Add the `Gadget`s to their `Owner`.
185 //! let mut gadgets = gadget_owner.gadgets.borrow_mut();
186 //! gadgets.push(Rc::downgrade(&gadget1));
187 //! gadgets.push(Rc::downgrade(&gadget2));
189 //! // `RefCell` dynamic borrow ends here.
192 //! // Iterate over our `Gadget`s, printing their details out.
193 //! for gadget_weak in gadget_owner.gadgets.borrow().iter() {
195 //! // `gadget_weak` is a `Weak<Gadget>`. Since `Weak` pointers can't
196 //! // guarantee the value is still allocated, we need to call
197 //! // `upgrade`, which returns an `Option<Rc<Gadget>>`.
199 //! // In this case we know the value still exists, so we simply
200 //! // `unwrap` the `Option`. In a more complicated program, you might
201 //! // need graceful error handling for a `None` result.
203 //! let gadget = gadget_weak.upgrade().unwrap();
204 //! println!("Gadget {} owned by {}", gadget.id, gadget.owner.name);
207 //! // At the end of the function, `gadget_owner`, `gadget1`, and `gadget2`
208 //! // are destroyed. There are now no strong (`Rc`) pointers to the
209 //! // gadgets, so they are destroyed. This zeroes the reference count on
210 //! // Gadget Man, so he gets destroyed as well.
214 //! [`Rc`]: struct.Rc.html
215 //! [`Weak`]: struct.Weak.html
216 //! [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
217 //! [`Cell`]: ../../std/cell/struct.Cell.html
218 //! [`RefCell`]: ../../std/cell/struct.RefCell.html
219 //! [send]: ../../std/marker/trait.Send.html
220 //! [arc]: ../../std/sync/struct.Arc.html
221 //! [`Deref`]: ../../std/ops/trait.Deref.html
222 //! [downgrade]: struct.Rc.html#method.downgrade
223 //! [upgrade]: struct.Weak.html#method.upgrade
224 //! [`None`]: ../../std/option/enum.Option.html#variant.None
225 //! [mutability]: ../../std/cell/index.html#introducing-mutability-inside-of-something-immutable
227 #![stable(feature = "rust1", since = "1.0.0")]
230 use crate::boxed::Box;
236 use core::cell::Cell;
237 use core::cmp::Ordering;
239 use core::hash::{Hash, Hasher};
240 use core::intrinsics::abort;
241 use core::marker::{self, Unpin, Unsize, PhantomData};
242 use core::mem::{self, align_of_val, forget, size_of_val};
243 use core::ops::{Deref, Receiver, CoerceUnsized, DispatchFromDyn};
245 use core::ptr::{self, NonNull};
246 use core::slice::from_raw_parts_mut;
247 use core::convert::From;
250 use crate::alloc::{Global, Alloc, Layout, box_free, handle_alloc_error};
251 use crate::string::String;
254 struct RcBox<T: ?Sized> {
260 /// A single-threaded reference-counting pointer. 'Rc' stands for 'Reference
263 /// See the [module-level documentation](./index.html) for more details.
265 /// The inherent methods of `Rc` are all associated functions, which means
266 /// that you have to call them as e.g., [`Rc::get_mut(&mut value)`][get_mut] instead of
267 /// `value.get_mut()`. This avoids conflicts with methods of the inner
270 /// [get_mut]: #method.get_mut
271 #[cfg_attr(not(test), lang = "rc")]
272 #[stable(feature = "rust1", since = "1.0.0")]
273 pub struct Rc<T: ?Sized> {
274 ptr: NonNull<RcBox<T>>,
275 phantom: PhantomData<T>,
278 #[stable(feature = "rust1", since = "1.0.0")]
279 impl<T: ?Sized> !marker::Send for Rc<T> {}
280 #[stable(feature = "rust1", since = "1.0.0")]
281 impl<T: ?Sized> !marker::Sync for Rc<T> {}
283 #[unstable(feature = "coerce_unsized", issue = "27732")]
284 impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Rc<U>> for Rc<T> {}
286 #[unstable(feature = "dispatch_from_dyn", issue = "0")]
287 impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Rc<U>> for Rc<T> {}
290 /// Constructs a new `Rc<T>`.
297 /// let five = Rc::new(5);
299 #[stable(feature = "rust1", since = "1.0.0")]
300 pub fn new(value: T) -> Rc<T> {
302 // there is an implicit weak pointer owned by all the strong
303 // pointers, which ensures that the weak destructor never frees
304 // the allocation while the strong destructor is running, even
305 // if the weak pointer is stored inside the strong one.
306 ptr: Box::into_raw_non_null(box RcBox {
307 strong: Cell::new(1),
311 phantom: PhantomData,
315 /// Constructs a new `Pin<Rc<T>>`. If `T` does not implement `Unpin`, then
316 /// `value` will be pinned in memory and unable to be moved.
317 #[stable(feature = "pin", since = "1.33.0")]
318 pub fn pin(value: T) -> Pin<Rc<T>> {
319 unsafe { Pin::new_unchecked(Rc::new(value)) }
322 /// Returns the contained value, if the `Rc` has exactly one strong reference.
324 /// Otherwise, an [`Err`][result] is returned with the same `Rc` that was
327 /// This will succeed even if there are outstanding weak references.
329 /// [result]: ../../std/result/enum.Result.html
336 /// let x = Rc::new(3);
337 /// assert_eq!(Rc::try_unwrap(x), Ok(3));
339 /// let x = Rc::new(4);
340 /// let _y = Rc::clone(&x);
341 /// assert_eq!(*Rc::try_unwrap(x).unwrap_err(), 4);
344 #[stable(feature = "rc_unique", since = "1.4.0")]
345 pub fn try_unwrap(this: Self) -> Result<T, Self> {
346 if Rc::strong_count(&this) == 1 {
348 let val = ptr::read(&*this); // copy the contained object
350 // Indicate to Weaks that they can't be promoted by decrementing
351 // the strong count, and then remove the implicit "strong weak"
352 // pointer while also handling drop logic by just crafting a
355 let _weak = Weak { ptr: this.ptr };
365 impl<T: ?Sized> Rc<T> {
366 /// Consumes the `Rc`, returning the wrapped pointer.
368 /// To avoid a memory leak the pointer must be converted back to an `Rc` using
369 /// [`Rc::from_raw`][from_raw].
371 /// [from_raw]: struct.Rc.html#method.from_raw
378 /// let x = Rc::new(10);
379 /// let x_ptr = Rc::into_raw(x);
380 /// assert_eq!(unsafe { *x_ptr }, 10);
382 #[stable(feature = "rc_raw", since = "1.17.0")]
383 pub fn into_raw(this: Self) -> *const T {
384 let ptr: *const T = &*this;
389 /// Constructs an `Rc` from a raw pointer.
391 /// The raw pointer must have been previously returned by a call to a
392 /// [`Rc::into_raw`][into_raw].
394 /// This function is unsafe because improper use may lead to memory problems. For example, a
395 /// double-free may occur if the function is called twice on the same raw pointer.
397 /// [into_raw]: struct.Rc.html#method.into_raw
404 /// let x = Rc::new(10);
405 /// let x_ptr = Rc::into_raw(x);
408 /// // Convert back to an `Rc` to prevent leak.
409 /// let x = Rc::from_raw(x_ptr);
410 /// assert_eq!(*x, 10);
412 /// // Further calls to `Rc::from_raw(x_ptr)` would be memory unsafe.
415 /// // The memory was freed when `x` went out of scope above, so `x_ptr` is now dangling!
417 #[stable(feature = "rc_raw", since = "1.17.0")]
418 pub unsafe fn from_raw(ptr: *const T) -> Self {
419 // Align the unsized value to the end of the RcBox.
420 // Because it is ?Sized, it will always be the last field in memory.
421 let align = align_of_val(&*ptr);
422 let layout = Layout::new::<RcBox<()>>();
423 let offset = (layout.size() + layout.padding_needed_for(align)) as isize;
425 // Reverse the offset to find the original RcBox.
426 let fake_ptr = ptr as *mut RcBox<T>;
427 let rc_ptr = set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset));
430 ptr: NonNull::new_unchecked(rc_ptr),
431 phantom: PhantomData,
435 /// Consumes the `Rc`, returning the wrapped pointer as `NonNull<T>`.
440 /// #![feature(rc_into_raw_non_null)]
444 /// let x = Rc::new(10);
445 /// let ptr = Rc::into_raw_non_null(x);
446 /// let deref = unsafe { *ptr.as_ref() };
447 /// assert_eq!(deref, 10);
449 #[unstable(feature = "rc_into_raw_non_null", issue = "47336")]
451 pub fn into_raw_non_null(this: Self) -> NonNull<T> {
452 // safe because Rc guarantees its pointer is non-null
453 unsafe { NonNull::new_unchecked(Rc::into_raw(this) as *mut _) }
456 /// Creates a new [`Weak`][weak] pointer to this value.
458 /// [weak]: struct.Weak.html
465 /// let five = Rc::new(5);
467 /// let weak_five = Rc::downgrade(&five);
469 #[stable(feature = "rc_weak", since = "1.4.0")]
470 pub fn downgrade(this: &Self) -> Weak<T> {
472 // Make sure we do not create a dangling Weak
473 debug_assert!(!is_dangling(this.ptr));
474 Weak { ptr: this.ptr }
477 /// Gets the number of [`Weak`][weak] pointers to this value.
479 /// [weak]: struct.Weak.html
486 /// let five = Rc::new(5);
487 /// let _weak_five = Rc::downgrade(&five);
489 /// assert_eq!(1, Rc::weak_count(&five));
492 #[stable(feature = "rc_counts", since = "1.15.0")]
493 pub fn weak_count(this: &Self) -> usize {
497 /// Gets the number of strong (`Rc`) pointers to this value.
504 /// let five = Rc::new(5);
505 /// let _also_five = Rc::clone(&five);
507 /// assert_eq!(2, Rc::strong_count(&five));
510 #[stable(feature = "rc_counts", since = "1.15.0")]
511 pub fn strong_count(this: &Self) -> usize {
515 /// Returns `true` if there are no other `Rc` or [`Weak`][weak] pointers to
516 /// this inner value.
518 /// [weak]: struct.Weak.html
520 fn is_unique(this: &Self) -> bool {
521 Rc::weak_count(this) == 0 && Rc::strong_count(this) == 1
524 /// Returns a mutable reference to the inner value, if there are
525 /// no other `Rc` or [`Weak`][weak] pointers to the same value.
527 /// Returns [`None`] otherwise, because it is not safe to
528 /// mutate a shared value.
530 /// See also [`make_mut`][make_mut], which will [`clone`][clone]
531 /// the inner value when it's shared.
533 /// [weak]: struct.Weak.html
534 /// [`None`]: ../../std/option/enum.Option.html#variant.None
535 /// [make_mut]: struct.Rc.html#method.make_mut
536 /// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
543 /// let mut x = Rc::new(3);
544 /// *Rc::get_mut(&mut x).unwrap() = 4;
545 /// assert_eq!(*x, 4);
547 /// let _y = Rc::clone(&x);
548 /// assert!(Rc::get_mut(&mut x).is_none());
551 #[stable(feature = "rc_unique", since = "1.4.0")]
552 pub fn get_mut(this: &mut Self) -> Option<&mut T> {
553 if Rc::is_unique(this) {
555 Some(&mut this.ptr.as_mut().value)
563 #[stable(feature = "ptr_eq", since = "1.17.0")]
564 /// Returns `true` if the two `Rc`s point to the same value (not
565 /// just values that compare as equal).
572 /// let five = Rc::new(5);
573 /// let same_five = Rc::clone(&five);
574 /// let other_five = Rc::new(5);
576 /// assert!(Rc::ptr_eq(&five, &same_five));
577 /// assert!(!Rc::ptr_eq(&five, &other_five));
579 pub fn ptr_eq(this: &Self, other: &Self) -> bool {
580 this.ptr.as_ptr() == other.ptr.as_ptr()
584 impl<T: Clone> Rc<T> {
585 /// Makes a mutable reference into the given `Rc`.
587 /// If there are other `Rc` pointers to the same value, then `make_mut` will
588 /// [`clone`] the inner value to ensure unique ownership. This is also
589 /// referred to as clone-on-write.
591 /// If there are no other `Rc` pointers to this value, then [`Weak`]
592 /// pointers to this value will be dissassociated.
594 /// See also [`get_mut`], which will fail rather than cloning.
596 /// [`Weak`]: struct.Weak.html
597 /// [`clone`]: ../../std/clone/trait.Clone.html#tymethod.clone
598 /// [`get_mut`]: struct.Rc.html#method.get_mut
605 /// let mut data = Rc::new(5);
607 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
608 /// let mut other_data = Rc::clone(&data); // Won't clone inner data
609 /// *Rc::make_mut(&mut data) += 1; // Clones inner data
610 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
611 /// *Rc::make_mut(&mut other_data) *= 2; // Won't clone anything
613 /// // Now `data` and `other_data` point to different values.
614 /// assert_eq!(*data, 8);
615 /// assert_eq!(*other_data, 12);
618 /// [`Weak`] pointers will be dissassociated:
623 /// let mut data = Rc::new(75);
624 /// let weak = Rc::downgrade(&data);
626 /// assert!(75 == *data);
627 /// assert!(75 == *weak.upgrade().unwrap());
629 /// *Rc::make_mut(&mut data) += 1;
631 /// assert!(76 == *data);
632 /// assert!(weak.upgrade().is_none());
635 #[stable(feature = "rc_unique", since = "1.4.0")]
636 pub fn make_mut(this: &mut Self) -> &mut T {
637 if Rc::strong_count(this) != 1 {
638 // Gotta clone the data, there are other Rcs
639 *this = Rc::new((**this).clone())
640 } else if Rc::weak_count(this) != 0 {
641 // Can just steal the data, all that's left is Weaks
643 let mut swap = Rc::new(ptr::read(&this.ptr.as_ref().value));
644 mem::swap(this, &mut swap);
646 // Remove implicit strong-weak ref (no need to craft a fake
647 // Weak here -- we know other Weaks can clean up for us)
652 // This unsafety is ok because we're guaranteed that the pointer
653 // returned is the *only* pointer that will ever be returned to T. Our
654 // reference count is guaranteed to be 1 at this point, and we required
655 // the `Rc<T>` itself to be `mut`, so we're returning the only possible
656 // reference to the inner value.
658 &mut this.ptr.as_mut().value
665 #[stable(feature = "rc_downcast", since = "1.29.0")]
666 /// Attempt to downcast the `Rc<dyn Any>` to a concrete type.
671 /// use std::any::Any;
674 /// fn print_if_string(value: Rc<dyn Any>) {
675 /// if let Ok(string) = value.downcast::<String>() {
676 /// println!("String ({}): {}", string.len(), string);
681 /// let my_string = "Hello World".to_string();
682 /// print_if_string(Rc::new(my_string));
683 /// print_if_string(Rc::new(0i8));
686 pub fn downcast<T: Any>(self) -> Result<Rc<T>, Rc<dyn Any>> {
687 if (*self).is::<T>() {
688 let ptr = self.ptr.cast::<RcBox<T>>();
690 Ok(Rc { ptr, phantom: PhantomData })
697 impl<T: ?Sized> Rc<T> {
698 // Allocates an `RcBox<T>` with sufficient space for an unsized value
699 unsafe fn allocate_for_ptr(ptr: *const T) -> *mut RcBox<T> {
700 // Calculate layout using the given value.
701 // Previously, layout was calculated on the expression
702 // `&*(ptr as *const RcBox<T>)`, but this created a misaligned
703 // reference (see #54908).
704 let layout = Layout::new::<RcBox<()>>()
705 .extend(Layout::for_value(&*ptr)).unwrap().0
706 .pad_to_align().unwrap();
708 let mem = Global.alloc(layout)
709 .unwrap_or_else(|_| handle_alloc_error(layout));
711 // Initialize the RcBox
712 let inner = set_data_ptr(ptr as *mut T, mem.as_ptr() as *mut u8) as *mut RcBox<T>;
713 debug_assert_eq!(Layout::for_value(&*inner), layout);
715 ptr::write(&mut (*inner).strong, Cell::new(1));
716 ptr::write(&mut (*inner).weak, Cell::new(1));
721 fn from_box(v: Box<T>) -> Rc<T> {
723 let box_unique = Box::into_unique(v);
724 let bptr = box_unique.as_ptr();
726 let value_size = size_of_val(&*bptr);
727 let ptr = Self::allocate_for_ptr(bptr);
729 // Copy value as bytes
730 ptr::copy_nonoverlapping(
731 bptr as *const T as *const u8,
732 &mut (*ptr).value as *mut _ as *mut u8,
735 // Free the allocation without dropping its contents
736 box_free(box_unique);
738 Rc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
743 // Sets the data pointer of a `?Sized` raw pointer.
745 // For a slice/trait object, this sets the `data` field and leaves the rest
746 // unchanged. For a sized raw pointer, this simply sets the pointer.
747 unsafe fn set_data_ptr<T: ?Sized, U>(mut ptr: *mut T, data: *mut U) -> *mut T {
748 ptr::write(&mut ptr as *mut _ as *mut *mut u8, data as *mut u8);
753 // Copy elements from slice into newly allocated Rc<[T]>
755 // Unsafe because the caller must either take ownership or bind `T: Copy`
756 unsafe fn copy_from_slice(v: &[T]) -> Rc<[T]> {
757 let v_ptr = v as *const [T];
758 let ptr = Self::allocate_for_ptr(v_ptr);
760 ptr::copy_nonoverlapping(
762 &mut (*ptr).value as *mut [T] as *mut T,
765 Rc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
769 trait RcFromSlice<T> {
770 fn from_slice(slice: &[T]) -> Self;
773 impl<T: Clone> RcFromSlice<T> for Rc<[T]> {
775 default fn from_slice(v: &[T]) -> Self {
776 // Panic guard while cloning T elements.
777 // In the event of a panic, elements that have been written
778 // into the new RcBox will be dropped, then the memory freed.
786 impl<T> Drop for Guard<T> {
789 let slice = from_raw_parts_mut(self.elems, self.n_elems);
790 ptr::drop_in_place(slice);
792 Global.dealloc(self.mem, self.layout.clone());
798 let v_ptr = v as *const [T];
799 let ptr = Self::allocate_for_ptr(v_ptr);
801 let mem = ptr as *mut _ as *mut u8;
802 let layout = Layout::for_value(&*ptr);
804 // Pointer to first element
805 let elems = &mut (*ptr).value as *mut [T] as *mut T;
807 let mut guard = Guard{
808 mem: NonNull::new_unchecked(mem),
814 for (i, item) in v.iter().enumerate() {
815 ptr::write(elems.add(i), item.clone());
819 // All clear. Forget the guard so it doesn't free the new RcBox.
822 Rc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
827 impl<T: Copy> RcFromSlice<T> for Rc<[T]> {
829 fn from_slice(v: &[T]) -> Self {
830 unsafe { Rc::copy_from_slice(v) }
834 #[stable(feature = "rust1", since = "1.0.0")]
835 impl<T: ?Sized> Deref for Rc<T> {
839 fn deref(&self) -> &T {
844 #[unstable(feature = "receiver_trait", issue = "0")]
845 impl<T: ?Sized> Receiver for Rc<T> {}
847 #[stable(feature = "rust1", since = "1.0.0")]
848 unsafe impl<#[may_dangle] T: ?Sized> Drop for Rc<T> {
851 /// This will decrement the strong reference count. If the strong reference
852 /// count reaches zero then the only other references (if any) are
853 /// [`Weak`], so we `drop` the inner value.
862 /// impl Drop for Foo {
863 /// fn drop(&mut self) {
864 /// println!("dropped!");
868 /// let foo = Rc::new(Foo);
869 /// let foo2 = Rc::clone(&foo);
871 /// drop(foo); // Doesn't print anything
872 /// drop(foo2); // Prints "dropped!"
875 /// [`Weak`]: ../../std/rc/struct.Weak.html
879 if self.strong() == 0 {
880 // destroy the contained object
881 ptr::drop_in_place(self.ptr.as_mut());
883 // remove the implicit "strong weak" pointer now that we've
884 // destroyed the contents.
887 if self.weak() == 0 {
888 Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref()));
895 #[stable(feature = "rust1", since = "1.0.0")]
896 impl<T: ?Sized> Clone for Rc<T> {
897 /// Makes a clone of the `Rc` pointer.
899 /// This creates another pointer to the same inner value, increasing the
900 /// strong reference count.
907 /// let five = Rc::new(5);
909 /// let _ = Rc::clone(&five);
912 fn clone(&self) -> Rc<T> {
914 Rc { ptr: self.ptr, phantom: PhantomData }
918 #[stable(feature = "rust1", since = "1.0.0")]
919 impl<T: Default> Default for Rc<T> {
920 /// Creates a new `Rc<T>`, with the `Default` value for `T`.
927 /// let x: Rc<i32> = Default::default();
928 /// assert_eq!(*x, 0);
931 fn default() -> Rc<T> {
932 Rc::new(Default::default())
936 #[stable(feature = "rust1", since = "1.0.0")]
937 trait RcEqIdent<T: ?Sized + PartialEq> {
938 fn eq(&self, other: &Rc<T>) -> bool;
939 fn ne(&self, other: &Rc<T>) -> bool;
942 #[stable(feature = "rust1", since = "1.0.0")]
943 impl<T: ?Sized + PartialEq> RcEqIdent<T> for Rc<T> {
945 default fn eq(&self, other: &Rc<T>) -> bool {
950 default fn ne(&self, other: &Rc<T>) -> bool {
955 /// We're doing this specialization here, and not as a more general optimization on `&T`, because it
956 /// would otherwise add a cost to all equality checks on refs. We assume that `Rc`s are used to
957 /// store large values, that are slow to clone, but also heavy to check for equality, causing this
958 /// cost to pay off more easily. It's also more likely to have two `Rc` clones, that point to
959 /// the same value, than two `&T`s.
960 #[stable(feature = "rust1", since = "1.0.0")]
961 impl<T: ?Sized + Eq> RcEqIdent<T> for Rc<T> {
963 fn eq(&self, other: &Rc<T>) -> bool {
964 Rc::ptr_eq(self, other) || **self == **other
968 fn ne(&self, other: &Rc<T>) -> bool {
969 !Rc::ptr_eq(self, other) && **self != **other
973 #[stable(feature = "rust1", since = "1.0.0")]
974 impl<T: ?Sized + PartialEq> PartialEq for Rc<T> {
975 /// Equality for two `Rc`s.
977 /// Two `Rc`s are equal if their inner values are equal.
979 /// If `T` also implements `Eq`, two `Rc`s that point to the same value are
987 /// let five = Rc::new(5);
989 /// assert!(five == Rc::new(5));
992 fn eq(&self, other: &Rc<T>) -> bool {
993 RcEqIdent::eq(self, other)
996 /// Inequality for two `Rc`s.
998 /// Two `Rc`s are unequal if their inner values are unequal.
1000 /// If `T` also implements `Eq`, two `Rc`s that point to the same value are
1006 /// use std::rc::Rc;
1008 /// let five = Rc::new(5);
1010 /// assert!(five != Rc::new(6));
1013 fn ne(&self, other: &Rc<T>) -> bool {
1014 RcEqIdent::ne(self, other)
1018 #[stable(feature = "rust1", since = "1.0.0")]
1019 impl<T: ?Sized + Eq> Eq for Rc<T> {}
1021 #[stable(feature = "rust1", since = "1.0.0")]
1022 impl<T: ?Sized + PartialOrd> PartialOrd for Rc<T> {
1023 /// Partial comparison for two `Rc`s.
1025 /// The two are compared by calling `partial_cmp()` on their inner values.
1030 /// use std::rc::Rc;
1031 /// use std::cmp::Ordering;
1033 /// let five = Rc::new(5);
1035 /// assert_eq!(Some(Ordering::Less), five.partial_cmp(&Rc::new(6)));
1038 fn partial_cmp(&self, other: &Rc<T>) -> Option<Ordering> {
1039 (**self).partial_cmp(&**other)
1042 /// Less-than comparison for two `Rc`s.
1044 /// The two are compared by calling `<` on their inner values.
1049 /// use std::rc::Rc;
1051 /// let five = Rc::new(5);
1053 /// assert!(five < Rc::new(6));
1056 fn lt(&self, other: &Rc<T>) -> bool {
1060 /// 'Less than or equal to' comparison for two `Rc`s.
1062 /// The two are compared by calling `<=` on their inner values.
1067 /// use std::rc::Rc;
1069 /// let five = Rc::new(5);
1071 /// assert!(five <= Rc::new(5));
1074 fn le(&self, other: &Rc<T>) -> bool {
1078 /// Greater-than comparison for two `Rc`s.
1080 /// The two are compared by calling `>` on their inner values.
1085 /// use std::rc::Rc;
1087 /// let five = Rc::new(5);
1089 /// assert!(five > Rc::new(4));
1092 fn gt(&self, other: &Rc<T>) -> bool {
1096 /// 'Greater than or equal to' comparison for two `Rc`s.
1098 /// The two are compared by calling `>=` on their inner values.
1103 /// use std::rc::Rc;
1105 /// let five = Rc::new(5);
1107 /// assert!(five >= Rc::new(5));
1110 fn ge(&self, other: &Rc<T>) -> bool {
1115 #[stable(feature = "rust1", since = "1.0.0")]
1116 impl<T: ?Sized + Ord> Ord for Rc<T> {
1117 /// Comparison for two `Rc`s.
1119 /// The two are compared by calling `cmp()` on their inner values.
1124 /// use std::rc::Rc;
1125 /// use std::cmp::Ordering;
1127 /// let five = Rc::new(5);
1129 /// assert_eq!(Ordering::Less, five.cmp(&Rc::new(6)));
1132 fn cmp(&self, other: &Rc<T>) -> Ordering {
1133 (**self).cmp(&**other)
1137 #[stable(feature = "rust1", since = "1.0.0")]
1138 impl<T: ?Sized + Hash> Hash for Rc<T> {
1139 fn hash<H: Hasher>(&self, state: &mut H) {
1140 (**self).hash(state);
1144 #[stable(feature = "rust1", since = "1.0.0")]
1145 impl<T: ?Sized + fmt::Display> fmt::Display for Rc<T> {
1146 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1147 fmt::Display::fmt(&**self, f)
1151 #[stable(feature = "rust1", since = "1.0.0")]
1152 impl<T: ?Sized + fmt::Debug> fmt::Debug for Rc<T> {
1153 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1154 fmt::Debug::fmt(&**self, f)
1158 #[stable(feature = "rust1", since = "1.0.0")]
1159 impl<T: ?Sized> fmt::Pointer for Rc<T> {
1160 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1161 fmt::Pointer::fmt(&(&**self as *const T), f)
1165 #[stable(feature = "from_for_ptrs", since = "1.6.0")]
1166 impl<T> From<T> for Rc<T> {
1167 fn from(t: T) -> Self {
1172 #[stable(feature = "shared_from_slice", since = "1.21.0")]
1173 impl<T: Clone> From<&[T]> for Rc<[T]> {
1175 fn from(v: &[T]) -> Rc<[T]> {
1176 <Self as RcFromSlice<T>>::from_slice(v)
1180 #[stable(feature = "shared_from_slice", since = "1.21.0")]
1181 impl From<&str> for Rc<str> {
1183 fn from(v: &str) -> Rc<str> {
1184 let rc = Rc::<[u8]>::from(v.as_bytes());
1185 unsafe { Rc::from_raw(Rc::into_raw(rc) as *const str) }
1189 #[stable(feature = "shared_from_slice", since = "1.21.0")]
1190 impl From<String> for Rc<str> {
1192 fn from(v: String) -> Rc<str> {
1197 #[stable(feature = "shared_from_slice", since = "1.21.0")]
1198 impl<T: ?Sized> From<Box<T>> for Rc<T> {
1200 fn from(v: Box<T>) -> Rc<T> {
1205 #[stable(feature = "shared_from_slice", since = "1.21.0")]
1206 impl<T> From<Vec<T>> for Rc<[T]> {
1208 fn from(mut v: Vec<T>) -> Rc<[T]> {
1210 let rc = Rc::copy_from_slice(&v);
1212 // Allow the Vec to free its memory, but not destroy its contents
1220 /// `Weak` is a version of [`Rc`] that holds a non-owning reference to the
1221 /// managed value. The value is accessed by calling [`upgrade`] on the `Weak`
1222 /// pointer, which returns an [`Option`]`<`[`Rc`]`<T>>`.
1224 /// Since a `Weak` reference does not count towards ownership, it will not
1225 /// prevent the inner value from being dropped, and `Weak` itself makes no
1226 /// guarantees about the value still being present and may return [`None`]
1227 /// when [`upgrade`]d.
1229 /// A `Weak` pointer is useful for keeping a temporary reference to the value
1230 /// within [`Rc`] without extending its lifetime. It is also used to prevent
1231 /// circular references between [`Rc`] pointers, since mutual owning references
1232 /// would never allow either [`Rc`] to be dropped. For example, a tree could
1233 /// have strong [`Rc`] pointers from parent nodes to children, and `Weak`
1234 /// pointers from children back to their parents.
1236 /// The typical way to obtain a `Weak` pointer is to call [`Rc::downgrade`].
1238 /// [`Rc`]: struct.Rc.html
1239 /// [`Rc::downgrade`]: struct.Rc.html#method.downgrade
1240 /// [`upgrade`]: struct.Weak.html#method.upgrade
1241 /// [`Option`]: ../../std/option/enum.Option.html
1242 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1243 #[stable(feature = "rc_weak", since = "1.4.0")]
1244 pub struct Weak<T: ?Sized> {
1245 // This is a `NonNull` to allow optimizing the size of this type in enums,
1246 // but it is not necessarily a valid pointer.
1247 // `Weak::new` sets this to `usize::MAX` so that it doesn’t need
1248 // to allocate space on the heap. That's not a value a real pointer
1249 // will ever have because RcBox has alignment at least 2.
1250 ptr: NonNull<RcBox<T>>,
1253 #[stable(feature = "rc_weak", since = "1.4.0")]
1254 impl<T: ?Sized> !marker::Send for Weak<T> {}
1255 #[stable(feature = "rc_weak", since = "1.4.0")]
1256 impl<T: ?Sized> !marker::Sync for Weak<T> {}
1258 #[unstable(feature = "coerce_unsized", issue = "27732")]
1259 impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {}
1261 #[unstable(feature = "dispatch_from_dyn", issue = "0")]
1262 impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Weak<U>> for Weak<T> {}
1265 /// Constructs a new `Weak<T>`, without allocating any memory.
1266 /// Calling [`upgrade`] on the return value always gives [`None`].
1268 /// [`upgrade`]: #method.upgrade
1269 /// [`None`]: ../../std/option/enum.Option.html
1274 /// use std::rc::Weak;
1276 /// let empty: Weak<i64> = Weak::new();
1277 /// assert!(empty.upgrade().is_none());
1279 #[stable(feature = "downgraded_weak", since = "1.10.0")]
1280 pub fn new() -> Weak<T> {
1282 ptr: NonNull::new(usize::MAX as *mut RcBox<T>).expect("MAX is not 0"),
1287 pub(crate) fn is_dangling<T: ?Sized>(ptr: NonNull<T>) -> bool {
1288 let address = ptr.as_ptr() as *mut () as usize;
1289 address == usize::MAX
1292 impl<T: ?Sized> Weak<T> {
1293 /// Attempts to upgrade the `Weak` pointer to an [`Rc`], extending
1294 /// the lifetime of the value if successful.
1296 /// Returns [`None`] if the value has since been dropped.
1298 /// [`Rc`]: struct.Rc.html
1299 /// [`None`]: ../../std/option/enum.Option.html
1304 /// use std::rc::Rc;
1306 /// let five = Rc::new(5);
1308 /// let weak_five = Rc::downgrade(&five);
1310 /// let strong_five: Option<Rc<_>> = weak_five.upgrade();
1311 /// assert!(strong_five.is_some());
1313 /// // Destroy all strong pointers.
1314 /// drop(strong_five);
1317 /// assert!(weak_five.upgrade().is_none());
1319 #[stable(feature = "rc_weak", since = "1.4.0")]
1320 pub fn upgrade(&self) -> Option<Rc<T>> {
1321 let inner = self.inner()?;
1322 if inner.strong() == 0 {
1326 Some(Rc { ptr: self.ptr, phantom: PhantomData })
1330 /// Gets the number of strong (`Rc`) pointers pointing to this value.
1332 /// If `self` was created using [`Weak::new`], this will return 0.
1334 /// [`Weak::new`]: #method.new
1335 #[unstable(feature = "weak_counts", issue = "57977")]
1336 pub fn strong_count(&self) -> usize {
1337 if let Some(inner) = self.inner() {
1344 /// Gets the number of `Weak` pointers pointing to this value.
1346 /// If `self` was created using [`Weak::new`], this will return `None`. If
1347 /// not, the returned value is at least 1, since `self` still points to the
1350 /// [`Weak::new`]: #method.new
1351 #[unstable(feature = "weak_counts", issue = "57977")]
1352 pub fn weak_count(&self) -> Option<usize> {
1353 self.inner().map(|inner| {
1354 if inner.strong() > 0 {
1355 inner.weak() - 1 // subtract the implicit weak ptr
1362 /// Returns `None` when the pointer is dangling and there is no allocated `RcBox`
1363 /// (i.e., when this `Weak` was created by `Weak::new`).
1365 fn inner(&self) -> Option<&RcBox<T>> {
1366 if is_dangling(self.ptr) {
1369 Some(unsafe { self.ptr.as_ref() })
1373 /// Returns `true` if the two `Weak`s point to the same value (not just values
1374 /// that compare as equal).
1378 /// Since this compares pointers it means that `Weak::new()` will equal each
1379 /// other, even though they don't point to any value.
1384 /// #![feature(weak_ptr_eq)]
1385 /// use std::rc::{Rc, Weak};
1387 /// let first_rc = Rc::new(5);
1388 /// let first = Rc::downgrade(&first_rc);
1389 /// let second = Rc::downgrade(&first_rc);
1391 /// assert!(Weak::ptr_eq(&first, &second));
1393 /// let third_rc = Rc::new(5);
1394 /// let third = Rc::downgrade(&third_rc);
1396 /// assert!(!Weak::ptr_eq(&first, &third));
1399 /// Comparing `Weak::new`.
1402 /// #![feature(weak_ptr_eq)]
1403 /// use std::rc::{Rc, Weak};
1405 /// let first = Weak::new();
1406 /// let second = Weak::new();
1407 /// assert!(Weak::ptr_eq(&first, &second));
1409 /// let third_rc = Rc::new(());
1410 /// let third = Rc::downgrade(&third_rc);
1411 /// assert!(!Weak::ptr_eq(&first, &third));
1414 #[unstable(feature = "weak_ptr_eq", issue = "55981")]
1415 pub fn ptr_eq(this: &Self, other: &Self) -> bool {
1416 this.ptr.as_ptr() == other.ptr.as_ptr()
1420 #[stable(feature = "rc_weak", since = "1.4.0")]
1421 impl<T: ?Sized> Drop for Weak<T> {
1422 /// Drops the `Weak` pointer.
1427 /// use std::rc::{Rc, Weak};
1431 /// impl Drop for Foo {
1432 /// fn drop(&mut self) {
1433 /// println!("dropped!");
1437 /// let foo = Rc::new(Foo);
1438 /// let weak_foo = Rc::downgrade(&foo);
1439 /// let other_weak_foo = Weak::clone(&weak_foo);
1441 /// drop(weak_foo); // Doesn't print anything
1442 /// drop(foo); // Prints "dropped!"
1444 /// assert!(other_weak_foo.upgrade().is_none());
1446 fn drop(&mut self) {
1447 if let Some(inner) = self.inner() {
1449 // the weak count starts at 1, and will only go to zero if all
1450 // the strong pointers have disappeared.
1451 if inner.weak() == 0 {
1453 Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref()));
1460 #[stable(feature = "rc_weak", since = "1.4.0")]
1461 impl<T: ?Sized> Clone for Weak<T> {
1462 /// Makes a clone of the `Weak` pointer that points to the same value.
1467 /// use std::rc::{Rc, Weak};
1469 /// let weak_five = Rc::downgrade(&Rc::new(5));
1471 /// let _ = Weak::clone(&weak_five);
1474 fn clone(&self) -> Weak<T> {
1475 if let Some(inner) = self.inner() {
1478 Weak { ptr: self.ptr }
1482 #[stable(feature = "rc_weak", since = "1.4.0")]
1483 impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> {
1484 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1489 #[stable(feature = "downgraded_weak", since = "1.10.0")]
1490 impl<T> Default for Weak<T> {
1491 /// Constructs a new `Weak<T>`, allocating memory for `T` without initializing
1492 /// it. Calling [`upgrade`] on the return value always gives [`None`].
1494 /// [`None`]: ../../std/option/enum.Option.html
1495 /// [`upgrade`]: ../../std/rc/struct.Weak.html#method.upgrade
1500 /// use std::rc::Weak;
1502 /// let empty: Weak<i64> = Default::default();
1503 /// assert!(empty.upgrade().is_none());
1505 fn default() -> Weak<T> {
1510 // NOTE: We checked_add here to deal with mem::forget safely. In particular
1511 // if you mem::forget Rcs (or Weaks), the ref-count can overflow, and then
1512 // you can free the allocation while outstanding Rcs (or Weaks) exist.
1513 // We abort because this is such a degenerate scenario that we don't care about
1514 // what happens -- no real program should ever experience this.
1516 // This should have negligible overhead since you don't actually need to
1517 // clone these much in Rust thanks to ownership and move-semantics.
1520 trait RcBoxPtr<T: ?Sized> {
1521 fn inner(&self) -> &RcBox<T>;
1524 fn strong(&self) -> usize {
1525 self.inner().strong.get()
1529 fn inc_strong(&self) {
1530 // We want to abort on overflow instead of dropping the value.
1531 // The reference count will never be zero when this is called;
1532 // nevertheless, we insert an abort here to hint LLVM at
1533 // an otherwise missed optimization.
1534 if self.strong() == 0 || self.strong() == usize::max_value() {
1537 self.inner().strong.set(self.strong() + 1);
1541 fn dec_strong(&self) {
1542 self.inner().strong.set(self.strong() - 1);
1546 fn weak(&self) -> usize {
1547 self.inner().weak.get()
1551 fn inc_weak(&self) {
1552 // We want to abort on overflow instead of dropping the value.
1553 // The reference count will never be zero when this is called;
1554 // nevertheless, we insert an abort here to hint LLVM at
1555 // an otherwise missed optimization.
1556 if self.weak() == 0 || self.weak() == usize::max_value() {
1559 self.inner().weak.set(self.weak() + 1);
1563 fn dec_weak(&self) {
1564 self.inner().weak.set(self.weak() - 1);
1568 impl<T: ?Sized> RcBoxPtr<T> for Rc<T> {
1570 fn inner(&self) -> &RcBox<T> {
1577 impl<T: ?Sized> RcBoxPtr<T> for RcBox<T> {
1579 fn inner(&self) -> &RcBox<T> {
1586 use super::{Rc, Weak};
1587 use std::boxed::Box;
1588 use std::cell::RefCell;
1589 use std::option::Option::{self, None, Some};
1590 use std::result::Result::{Err, Ok};
1592 use std::clone::Clone;
1593 use std::convert::From;
1597 let x = Rc::new(RefCell::new(5));
1599 *x.borrow_mut() = 20;
1600 assert_eq!(*y.borrow(), 20);
1610 fn test_simple_clone() {
1618 fn test_destructor() {
1619 let x: Rc<Box<_>> = Rc::new(box 5);
1626 let y = Rc::downgrade(&x);
1627 assert!(y.upgrade().is_some());
1633 let y = Rc::downgrade(&x);
1635 assert!(y.upgrade().is_none());
1639 fn weak_self_cyclic() {
1641 x: RefCell<Option<Weak<Cycle>>>,
1644 let a = Rc::new(Cycle { x: RefCell::new(None) });
1645 let b = Rc::downgrade(&a.clone());
1646 *a.x.borrow_mut() = Some(b);
1648 // hopefully we don't double-free (or leak)...
1654 assert!(Rc::is_unique(&x));
1656 assert!(!Rc::is_unique(&x));
1658 assert!(Rc::is_unique(&x));
1659 let w = Rc::downgrade(&x);
1660 assert!(!Rc::is_unique(&x));
1662 assert!(Rc::is_unique(&x));
1666 fn test_strong_count() {
1668 assert!(Rc::strong_count(&a) == 1);
1669 let w = Rc::downgrade(&a);
1670 assert!(Rc::strong_count(&a) == 1);
1671 let b = w.upgrade().expect("upgrade of live rc failed");
1672 assert!(Rc::strong_count(&b) == 2);
1673 assert!(Rc::strong_count(&a) == 2);
1676 assert!(Rc::strong_count(&b) == 1);
1678 assert!(Rc::strong_count(&b) == 2);
1679 assert!(Rc::strong_count(&c) == 2);
1683 fn test_weak_count() {
1685 assert!(Rc::strong_count(&a) == 1);
1686 assert!(Rc::weak_count(&a) == 0);
1687 let w = Rc::downgrade(&a);
1688 assert!(Rc::strong_count(&a) == 1);
1689 assert!(Rc::weak_count(&a) == 1);
1691 assert!(Rc::strong_count(&a) == 1);
1692 assert!(Rc::weak_count(&a) == 0);
1694 assert!(Rc::strong_count(&a) == 2);
1695 assert!(Rc::weak_count(&a) == 0);
1701 assert_eq!(Weak::weak_count(&Weak::<u64>::new()), None);
1702 assert_eq!(Weak::strong_count(&Weak::<u64>::new()), 0);
1705 let w = Rc::downgrade(&a);
1706 assert_eq!(Weak::strong_count(&w), 1);
1707 assert_eq!(Weak::weak_count(&w), Some(1));
1709 assert_eq!(Weak::strong_count(&w), 1);
1710 assert_eq!(Weak::weak_count(&w), Some(2));
1711 assert_eq!(Weak::strong_count(&w2), 1);
1712 assert_eq!(Weak::weak_count(&w2), Some(2));
1714 assert_eq!(Weak::strong_count(&w2), 1);
1715 assert_eq!(Weak::weak_count(&w2), Some(1));
1717 assert_eq!(Weak::strong_count(&w2), 2);
1718 assert_eq!(Weak::weak_count(&w2), Some(1));
1721 assert_eq!(Weak::strong_count(&w2), 0);
1722 assert_eq!(Weak::weak_count(&w2), Some(1));
1729 assert_eq!(Rc::try_unwrap(x), Ok(3));
1732 assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4)));
1734 let _w = Rc::downgrade(&x);
1735 assert_eq!(Rc::try_unwrap(x), Ok(5));
1739 fn into_from_raw() {
1740 let x = Rc::new(box "hello");
1743 let x_ptr = Rc::into_raw(x);
1746 assert_eq!(**x_ptr, "hello");
1748 let x = Rc::from_raw(x_ptr);
1749 assert_eq!(**x, "hello");
1751 assert_eq!(Rc::try_unwrap(x).map(|x| *x), Ok("hello"));
1756 fn test_into_from_raw_unsized() {
1757 use std::fmt::Display;
1758 use std::string::ToString;
1760 let rc: Rc<str> = Rc::from("foo");
1762 let ptr = Rc::into_raw(rc.clone());
1763 let rc2 = unsafe { Rc::from_raw(ptr) };
1765 assert_eq!(unsafe { &*ptr }, "foo");
1766 assert_eq!(rc, rc2);
1768 let rc: Rc<dyn Display> = Rc::new(123);
1770 let ptr = Rc::into_raw(rc.clone());
1771 let rc2 = unsafe { Rc::from_raw(ptr) };
1773 assert_eq!(unsafe { &*ptr }.to_string(), "123");
1774 assert_eq!(rc2.to_string(), "123");
1779 let mut x = Rc::new(3);
1780 *Rc::get_mut(&mut x).unwrap() = 4;
1783 assert!(Rc::get_mut(&mut x).is_none());
1785 assert!(Rc::get_mut(&mut x).is_some());
1786 let _w = Rc::downgrade(&x);
1787 assert!(Rc::get_mut(&mut x).is_none());
1791 fn test_cowrc_clone_make_unique() {
1792 let mut cow0 = Rc::new(75);
1793 let mut cow1 = cow0.clone();
1794 let mut cow2 = cow1.clone();
1796 assert!(75 == *Rc::make_mut(&mut cow0));
1797 assert!(75 == *Rc::make_mut(&mut cow1));
1798 assert!(75 == *Rc::make_mut(&mut cow2));
1800 *Rc::make_mut(&mut cow0) += 1;
1801 *Rc::make_mut(&mut cow1) += 2;
1802 *Rc::make_mut(&mut cow2) += 3;
1804 assert!(76 == *cow0);
1805 assert!(77 == *cow1);
1806 assert!(78 == *cow2);
1808 // none should point to the same backing memory
1809 assert!(*cow0 != *cow1);
1810 assert!(*cow0 != *cow2);
1811 assert!(*cow1 != *cow2);
1815 fn test_cowrc_clone_unique2() {
1816 let mut cow0 = Rc::new(75);
1817 let cow1 = cow0.clone();
1818 let cow2 = cow1.clone();
1820 assert!(75 == *cow0);
1821 assert!(75 == *cow1);
1822 assert!(75 == *cow2);
1824 *Rc::make_mut(&mut cow0) += 1;
1826 assert!(76 == *cow0);
1827 assert!(75 == *cow1);
1828 assert!(75 == *cow2);
1830 // cow1 and cow2 should share the same contents
1831 // cow0 should have a unique reference
1832 assert!(*cow0 != *cow1);
1833 assert!(*cow0 != *cow2);
1834 assert!(*cow1 == *cow2);
1838 fn test_cowrc_clone_weak() {
1839 let mut cow0 = Rc::new(75);
1840 let cow1_weak = Rc::downgrade(&cow0);
1842 assert!(75 == *cow0);
1843 assert!(75 == *cow1_weak.upgrade().unwrap());
1845 *Rc::make_mut(&mut cow0) += 1;
1847 assert!(76 == *cow0);
1848 assert!(cow1_weak.upgrade().is_none());
1853 let foo = Rc::new(75);
1854 assert_eq!(format!("{:?}", foo), "75");
1859 let foo: Rc<[i32]> = Rc::new([1, 2, 3]);
1860 assert_eq!(foo, foo.clone());
1864 fn test_from_owned() {
1866 let foo_rc = Rc::from(foo);
1867 assert!(123 == *foo_rc);
1871 fn test_new_weak() {
1872 let foo: Weak<usize> = Weak::new();
1873 assert!(foo.upgrade().is_none());
1878 let five = Rc::new(5);
1879 let same_five = five.clone();
1880 let other_five = Rc::new(5);
1882 assert!(Rc::ptr_eq(&five, &same_five));
1883 assert!(!Rc::ptr_eq(&five, &other_five));
1887 fn test_from_str() {
1888 let r: Rc<str> = Rc::from("foo");
1890 assert_eq!(&r[..], "foo");
1894 fn test_copy_from_slice() {
1895 let s: &[u32] = &[1, 2, 3];
1896 let r: Rc<[u32]> = Rc::from(s);
1898 assert_eq!(&r[..], [1, 2, 3]);
1902 fn test_clone_from_slice() {
1903 #[derive(Clone, Debug, Eq, PartialEq)]
1906 let s: &[X] = &[X(1), X(2), X(3)];
1907 let r: Rc<[X]> = Rc::from(s);
1909 assert_eq!(&r[..], s);
1914 fn test_clone_from_slice_panic() {
1915 use std::string::{String, ToString};
1917 struct Fail(u32, String);
1919 impl Clone for Fail {
1920 fn clone(&self) -> Fail {
1924 Fail(self.0, self.1.clone())
1929 Fail(0, "foo".to_string()),
1930 Fail(1, "bar".to_string()),
1931 Fail(2, "baz".to_string()),
1934 // Should panic, but not cause memory corruption
1935 let _r: Rc<[Fail]> = Rc::from(s);
1939 fn test_from_box() {
1940 let b: Box<u32> = box 123;
1941 let r: Rc<u32> = Rc::from(b);
1943 assert_eq!(*r, 123);
1947 fn test_from_box_str() {
1948 use std::string::String;
1950 let s = String::from("foo").into_boxed_str();
1951 let r: Rc<str> = Rc::from(s);
1953 assert_eq!(&r[..], "foo");
1957 fn test_from_box_slice() {
1958 let s = vec![1, 2, 3].into_boxed_slice();
1959 let r: Rc<[u32]> = Rc::from(s);
1961 assert_eq!(&r[..], [1, 2, 3]);
1965 fn test_from_box_trait() {
1966 use std::fmt::Display;
1967 use std::string::ToString;
1969 let b: Box<dyn Display> = box 123;
1970 let r: Rc<dyn Display> = Rc::from(b);
1972 assert_eq!(r.to_string(), "123");
1976 fn test_from_box_trait_zero_sized() {
1977 use std::fmt::Debug;
1979 let b: Box<dyn Debug> = box ();
1980 let r: Rc<dyn Debug> = Rc::from(b);
1982 assert_eq!(format!("{:?}", r), "()");
1986 fn test_from_vec() {
1987 let v = vec![1, 2, 3];
1988 let r: Rc<[u32]> = Rc::from(v);
1990 assert_eq!(&r[..], [1, 2, 3]);
1994 fn test_downcast() {
1997 let r1: Rc<dyn Any> = Rc::new(i32::max_value());
1998 let r2: Rc<dyn Any> = Rc::new("abc");
2000 assert!(r1.clone().downcast::<u32>().is_err());
2002 let r1i32 = r1.downcast::<i32>();
2003 assert!(r1i32.is_ok());
2004 assert_eq!(r1i32.unwrap(), Rc::new(i32::max_value()));
2006 assert!(r2.clone().downcast::<i32>().is_err());
2008 let r2str = r2.downcast::<&'static str>();
2009 assert!(r2str.is_ok());
2010 assert_eq!(r2str.unwrap(), Rc::new("abc"));
2014 #[stable(feature = "rust1", since = "1.0.0")]
2015 impl<T: ?Sized> borrow::Borrow<T> for Rc<T> {
2016 fn borrow(&self) -> &T {
2021 #[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
2022 impl<T: ?Sized> AsRef<T> for Rc<T> {
2023 fn as_ref(&self) -> &T {
2028 #[stable(feature = "pin", since = "1.33.0")]
2029 impl<T: ?Sized> Unpin for Rc<T> { }