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` or [`Weak`][weak] pointers to the same value,
588 /// then `make_mut` will invoke [`clone`][clone] on the inner value to
589 /// ensure unique ownership. This is also referred to as clone-on-write.
591 /// See also [`get_mut`][get_mut], which will fail rather than cloning.
593 /// [weak]: struct.Weak.html
594 /// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
595 /// [get_mut]: struct.Rc.html#method.get_mut
602 /// let mut data = Rc::new(5);
604 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
605 /// let mut other_data = Rc::clone(&data); // Won't clone inner data
606 /// *Rc::make_mut(&mut data) += 1; // Clones inner data
607 /// *Rc::make_mut(&mut data) += 1; // Won't clone anything
608 /// *Rc::make_mut(&mut other_data) *= 2; // Won't clone anything
610 /// // Now `data` and `other_data` point to different values.
611 /// assert_eq!(*data, 8);
612 /// assert_eq!(*other_data, 12);
615 #[stable(feature = "rc_unique", since = "1.4.0")]
616 pub fn make_mut(this: &mut Self) -> &mut T {
617 if Rc::strong_count(this) != 1 {
618 // Gotta clone the data, there are other Rcs
619 *this = Rc::new((**this).clone())
620 } else if Rc::weak_count(this) != 0 {
621 // Can just steal the data, all that's left is Weaks
623 let mut swap = Rc::new(ptr::read(&this.ptr.as_ref().value));
624 mem::swap(this, &mut swap);
626 // Remove implicit strong-weak ref (no need to craft a fake
627 // Weak here -- we know other Weaks can clean up for us)
632 // This unsafety is ok because we're guaranteed that the pointer
633 // returned is the *only* pointer that will ever be returned to T. Our
634 // reference count is guaranteed to be 1 at this point, and we required
635 // the `Rc<T>` itself to be `mut`, so we're returning the only possible
636 // reference to the inner value.
638 &mut this.ptr.as_mut().value
645 #[stable(feature = "rc_downcast", since = "1.29.0")]
646 /// Attempt to downcast the `Rc<dyn Any>` to a concrete type.
651 /// use std::any::Any;
654 /// fn print_if_string(value: Rc<dyn Any>) {
655 /// if let Ok(string) = value.downcast::<String>() {
656 /// println!("String ({}): {}", string.len(), string);
661 /// let my_string = "Hello World".to_string();
662 /// print_if_string(Rc::new(my_string));
663 /// print_if_string(Rc::new(0i8));
666 pub fn downcast<T: Any>(self) -> Result<Rc<T>, Rc<dyn Any>> {
667 if (*self).is::<T>() {
668 let ptr = self.ptr.cast::<RcBox<T>>();
670 Ok(Rc { ptr, phantom: PhantomData })
677 impl<T: ?Sized> Rc<T> {
678 // Allocates an `RcBox<T>` with sufficient space for an unsized value
679 unsafe fn allocate_for_ptr(ptr: *const T) -> *mut RcBox<T> {
680 // Calculate layout using the given value.
681 // Previously, layout was calculated on the expression
682 // `&*(ptr as *const RcBox<T>)`, but this created a misaligned
683 // reference (see #54908).
684 let layout = Layout::new::<RcBox<()>>()
685 .extend(Layout::for_value(&*ptr)).unwrap().0
686 .pad_to_align().unwrap();
688 let mem = Global.alloc(layout)
689 .unwrap_or_else(|_| handle_alloc_error(layout));
691 // Initialize the RcBox
692 let inner = set_data_ptr(ptr as *mut T, mem.as_ptr() as *mut u8) as *mut RcBox<T>;
693 debug_assert_eq!(Layout::for_value(&*inner), layout);
695 ptr::write(&mut (*inner).strong, Cell::new(1));
696 ptr::write(&mut (*inner).weak, Cell::new(1));
701 fn from_box(v: Box<T>) -> Rc<T> {
703 let box_unique = Box::into_unique(v);
704 let bptr = box_unique.as_ptr();
706 let value_size = size_of_val(&*bptr);
707 let ptr = Self::allocate_for_ptr(bptr);
709 // Copy value as bytes
710 ptr::copy_nonoverlapping(
711 bptr as *const T as *const u8,
712 &mut (*ptr).value as *mut _ as *mut u8,
715 // Free the allocation without dropping its contents
716 box_free(box_unique);
718 Rc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
723 // Sets the data pointer of a `?Sized` raw pointer.
725 // For a slice/trait object, this sets the `data` field and leaves the rest
726 // unchanged. For a sized raw pointer, this simply sets the pointer.
727 unsafe fn set_data_ptr<T: ?Sized, U>(mut ptr: *mut T, data: *mut U) -> *mut T {
728 ptr::write(&mut ptr as *mut _ as *mut *mut u8, data as *mut u8);
733 // Copy elements from slice into newly allocated Rc<[T]>
735 // Unsafe because the caller must either take ownership or bind `T: Copy`
736 unsafe fn copy_from_slice(v: &[T]) -> Rc<[T]> {
737 let v_ptr = v as *const [T];
738 let ptr = Self::allocate_for_ptr(v_ptr);
740 ptr::copy_nonoverlapping(
742 &mut (*ptr).value as *mut [T] as *mut T,
745 Rc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
749 trait RcFromSlice<T> {
750 fn from_slice(slice: &[T]) -> Self;
753 impl<T: Clone> RcFromSlice<T> for Rc<[T]> {
755 default fn from_slice(v: &[T]) -> Self {
756 // Panic guard while cloning T elements.
757 // In the event of a panic, elements that have been written
758 // into the new RcBox will be dropped, then the memory freed.
766 impl<T> Drop for Guard<T> {
769 let slice = from_raw_parts_mut(self.elems, self.n_elems);
770 ptr::drop_in_place(slice);
772 Global.dealloc(self.mem, self.layout.clone());
778 let v_ptr = v as *const [T];
779 let ptr = Self::allocate_for_ptr(v_ptr);
781 let mem = ptr as *mut _ as *mut u8;
782 let layout = Layout::for_value(&*ptr);
784 // Pointer to first element
785 let elems = &mut (*ptr).value as *mut [T] as *mut T;
787 let mut guard = Guard{
788 mem: NonNull::new_unchecked(mem),
794 for (i, item) in v.iter().enumerate() {
795 ptr::write(elems.add(i), item.clone());
799 // All clear. Forget the guard so it doesn't free the new RcBox.
802 Rc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
807 impl<T: Copy> RcFromSlice<T> for Rc<[T]> {
809 fn from_slice(v: &[T]) -> Self {
810 unsafe { Rc::copy_from_slice(v) }
814 #[stable(feature = "rust1", since = "1.0.0")]
815 impl<T: ?Sized> Deref for Rc<T> {
819 fn deref(&self) -> &T {
824 #[unstable(feature = "receiver_trait", issue = "0")]
825 impl<T: ?Sized> Receiver for Rc<T> {}
827 #[stable(feature = "rust1", since = "1.0.0")]
828 unsafe impl<#[may_dangle] T: ?Sized> Drop for Rc<T> {
831 /// This will decrement the strong reference count. If the strong reference
832 /// count reaches zero then the only other references (if any) are
833 /// [`Weak`], so we `drop` the inner value.
842 /// impl Drop for Foo {
843 /// fn drop(&mut self) {
844 /// println!("dropped!");
848 /// let foo = Rc::new(Foo);
849 /// let foo2 = Rc::clone(&foo);
851 /// drop(foo); // Doesn't print anything
852 /// drop(foo2); // Prints "dropped!"
855 /// [`Weak`]: ../../std/rc/struct.Weak.html
859 if self.strong() == 0 {
860 // destroy the contained object
861 ptr::drop_in_place(self.ptr.as_mut());
863 // remove the implicit "strong weak" pointer now that we've
864 // destroyed the contents.
867 if self.weak() == 0 {
868 Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref()));
875 #[stable(feature = "rust1", since = "1.0.0")]
876 impl<T: ?Sized> Clone for Rc<T> {
877 /// Makes a clone of the `Rc` pointer.
879 /// This creates another pointer to the same inner value, increasing the
880 /// strong reference count.
887 /// let five = Rc::new(5);
889 /// let _ = Rc::clone(&five);
892 fn clone(&self) -> Rc<T> {
894 Rc { ptr: self.ptr, phantom: PhantomData }
898 #[stable(feature = "rust1", since = "1.0.0")]
899 impl<T: Default> Default for Rc<T> {
900 /// Creates a new `Rc<T>`, with the `Default` value for `T`.
907 /// let x: Rc<i32> = Default::default();
908 /// assert_eq!(*x, 0);
911 fn default() -> Rc<T> {
912 Rc::new(Default::default())
916 #[stable(feature = "rust1", since = "1.0.0")]
917 trait RcEqIdent<T: ?Sized + PartialEq> {
918 fn eq(&self, other: &Rc<T>) -> bool;
919 fn ne(&self, other: &Rc<T>) -> bool;
922 #[stable(feature = "rust1", since = "1.0.0")]
923 impl<T: ?Sized + PartialEq> RcEqIdent<T> for Rc<T> {
925 default fn eq(&self, other: &Rc<T>) -> bool {
930 default fn ne(&self, other: &Rc<T>) -> bool {
935 #[stable(feature = "rust1", since = "1.0.0")]
936 impl<T: ?Sized + Eq> RcEqIdent<T> for Rc<T> {
938 fn eq(&self, other: &Rc<T>) -> bool {
939 Rc::ptr_eq(self, other) || **self == **other
943 fn ne(&self, other: &Rc<T>) -> bool {
944 !Rc::ptr_eq(self, other) && **self != **other
948 #[stable(feature = "rust1", since = "1.0.0")]
949 impl<T: ?Sized + PartialEq> PartialEq for Rc<T> {
950 /// Equality for two `Rc`s.
952 /// Two `Rc`s are equal if their inner values are equal.
954 /// If `T` also implements `Eq`, two `Rc`s that point to the same value are
962 /// let five = Rc::new(5);
964 /// assert!(five == Rc::new(5));
967 fn eq(&self, other: &Rc<T>) -> bool {
968 RcEqIdent::eq(self, other)
971 /// Inequality for two `Rc`s.
973 /// Two `Rc`s are unequal if their inner values are unequal.
975 /// If `T` also implements `Eq`, two `Rc`s that point to the same value are
983 /// let five = Rc::new(5);
985 /// assert!(five != Rc::new(6));
988 fn ne(&self, other: &Rc<T>) -> bool {
989 RcEqIdent::ne(self, other)
993 #[stable(feature = "rust1", since = "1.0.0")]
994 impl<T: ?Sized + Eq> Eq for Rc<T> {}
996 #[stable(feature = "rust1", since = "1.0.0")]
997 impl<T: ?Sized + PartialOrd> PartialOrd for Rc<T> {
998 /// Partial comparison for two `Rc`s.
1000 /// The two are compared by calling `partial_cmp()` on their inner values.
1005 /// use std::rc::Rc;
1006 /// use std::cmp::Ordering;
1008 /// let five = Rc::new(5);
1010 /// assert_eq!(Some(Ordering::Less), five.partial_cmp(&Rc::new(6)));
1013 fn partial_cmp(&self, other: &Rc<T>) -> Option<Ordering> {
1014 (**self).partial_cmp(&**other)
1017 /// Less-than comparison for two `Rc`s.
1019 /// The two are compared by calling `<` on their inner values.
1024 /// use std::rc::Rc;
1026 /// let five = Rc::new(5);
1028 /// assert!(five < Rc::new(6));
1031 fn lt(&self, other: &Rc<T>) -> bool {
1035 /// 'Less than or equal to' comparison for two `Rc`s.
1037 /// The two are compared by calling `<=` on their inner values.
1042 /// use std::rc::Rc;
1044 /// let five = Rc::new(5);
1046 /// assert!(five <= Rc::new(5));
1049 fn le(&self, other: &Rc<T>) -> bool {
1053 /// Greater-than comparison for two `Rc`s.
1055 /// The two are compared by calling `>` on their inner values.
1060 /// use std::rc::Rc;
1062 /// let five = Rc::new(5);
1064 /// assert!(five > Rc::new(4));
1067 fn gt(&self, other: &Rc<T>) -> bool {
1071 /// 'Greater than or equal to' comparison for two `Rc`s.
1073 /// The two are compared by calling `>=` on their inner values.
1078 /// use std::rc::Rc;
1080 /// let five = Rc::new(5);
1082 /// assert!(five >= Rc::new(5));
1085 fn ge(&self, other: &Rc<T>) -> bool {
1090 #[stable(feature = "rust1", since = "1.0.0")]
1091 impl<T: ?Sized + Ord> Ord for Rc<T> {
1092 /// Comparison for two `Rc`s.
1094 /// The two are compared by calling `cmp()` on their inner values.
1099 /// use std::rc::Rc;
1100 /// use std::cmp::Ordering;
1102 /// let five = Rc::new(5);
1104 /// assert_eq!(Ordering::Less, five.cmp(&Rc::new(6)));
1107 fn cmp(&self, other: &Rc<T>) -> Ordering {
1108 (**self).cmp(&**other)
1112 #[stable(feature = "rust1", since = "1.0.0")]
1113 impl<T: ?Sized + Hash> Hash for Rc<T> {
1114 fn hash<H: Hasher>(&self, state: &mut H) {
1115 (**self).hash(state);
1119 #[stable(feature = "rust1", since = "1.0.0")]
1120 impl<T: ?Sized + fmt::Display> fmt::Display for Rc<T> {
1121 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1122 fmt::Display::fmt(&**self, f)
1126 #[stable(feature = "rust1", since = "1.0.0")]
1127 impl<T: ?Sized + fmt::Debug> fmt::Debug for Rc<T> {
1128 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1129 fmt::Debug::fmt(&**self, f)
1133 #[stable(feature = "rust1", since = "1.0.0")]
1134 impl<T: ?Sized> fmt::Pointer for Rc<T> {
1135 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1136 fmt::Pointer::fmt(&(&**self as *const T), f)
1140 #[stable(feature = "from_for_ptrs", since = "1.6.0")]
1141 impl<T> From<T> for Rc<T> {
1142 fn from(t: T) -> Self {
1147 #[stable(feature = "shared_from_slice", since = "1.21.0")]
1148 impl<'a, T: Clone> From<&'a [T]> for Rc<[T]> {
1150 fn from(v: &[T]) -> Rc<[T]> {
1151 <Self as RcFromSlice<T>>::from_slice(v)
1155 #[stable(feature = "shared_from_slice", since = "1.21.0")]
1156 impl<'a> From<&'a str> for Rc<str> {
1158 fn from(v: &str) -> Rc<str> {
1159 let rc = Rc::<[u8]>::from(v.as_bytes());
1160 unsafe { Rc::from_raw(Rc::into_raw(rc) as *const str) }
1164 #[stable(feature = "shared_from_slice", since = "1.21.0")]
1165 impl From<String> for Rc<str> {
1167 fn from(v: String) -> Rc<str> {
1172 #[stable(feature = "shared_from_slice", since = "1.21.0")]
1173 impl<T: ?Sized> From<Box<T>> for Rc<T> {
1175 fn from(v: Box<T>) -> Rc<T> {
1180 #[stable(feature = "shared_from_slice", since = "1.21.0")]
1181 impl<T> From<Vec<T>> for Rc<[T]> {
1183 fn from(mut v: Vec<T>) -> Rc<[T]> {
1185 let rc = Rc::copy_from_slice(&v);
1187 // Allow the Vec to free its memory, but not destroy its contents
1195 /// `Weak` is a version of [`Rc`] that holds a non-owning reference to the
1196 /// managed value. The value is accessed by calling [`upgrade`] on the `Weak`
1197 /// pointer, which returns an [`Option`]`<`[`Rc`]`<T>>`.
1199 /// Since a `Weak` reference does not count towards ownership, it will not
1200 /// prevent the inner value from being dropped, and `Weak` itself makes no
1201 /// guarantees about the value still being present and may return [`None`]
1202 /// when [`upgrade`]d.
1204 /// A `Weak` pointer is useful for keeping a temporary reference to the value
1205 /// within [`Rc`] without extending its lifetime. It is also used to prevent
1206 /// circular references between [`Rc`] pointers, since mutual owning references
1207 /// would never allow either [`Rc`] to be dropped. For example, a tree could
1208 /// have strong [`Rc`] pointers from parent nodes to children, and `Weak`
1209 /// pointers from children back to their parents.
1211 /// The typical way to obtain a `Weak` pointer is to call [`Rc::downgrade`].
1213 /// [`Rc`]: struct.Rc.html
1214 /// [`Rc::downgrade`]: struct.Rc.html#method.downgrade
1215 /// [`upgrade`]: struct.Weak.html#method.upgrade
1216 /// [`Option`]: ../../std/option/enum.Option.html
1217 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1218 #[stable(feature = "rc_weak", since = "1.4.0")]
1219 pub struct Weak<T: ?Sized> {
1220 // This is a `NonNull` to allow optimizing the size of this type in enums,
1221 // but it is not necessarily a valid pointer.
1222 // `Weak::new` sets this to `usize::MAX` so that it doesn’t need
1223 // to allocate space on the heap. That's not a value a real pointer
1224 // will ever have because RcBox has alignment at least 2.
1225 ptr: NonNull<RcBox<T>>,
1228 #[stable(feature = "rc_weak", since = "1.4.0")]
1229 impl<T: ?Sized> !marker::Send for Weak<T> {}
1230 #[stable(feature = "rc_weak", since = "1.4.0")]
1231 impl<T: ?Sized> !marker::Sync for Weak<T> {}
1233 #[unstable(feature = "coerce_unsized", issue = "27732")]
1234 impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {}
1236 #[unstable(feature = "dispatch_from_dyn", issue = "0")]
1237 impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Weak<U>> for Weak<T> {}
1240 /// Constructs a new `Weak<T>`, without allocating any memory.
1241 /// Calling [`upgrade`] on the return value always gives [`None`].
1243 /// [`upgrade`]: #method.upgrade
1244 /// [`None`]: ../../std/option/enum.Option.html
1249 /// use std::rc::Weak;
1251 /// let empty: Weak<i64> = Weak::new();
1252 /// assert!(empty.upgrade().is_none());
1254 #[stable(feature = "downgraded_weak", since = "1.10.0")]
1255 pub fn new() -> Weak<T> {
1257 ptr: NonNull::new(usize::MAX as *mut RcBox<T>).expect("MAX is not 0"),
1262 pub(crate) fn is_dangling<T: ?Sized>(ptr: NonNull<T>) -> bool {
1263 let address = ptr.as_ptr() as *mut () as usize;
1264 address == usize::MAX
1267 impl<T: ?Sized> Weak<T> {
1268 /// Attempts to upgrade the `Weak` pointer to an [`Rc`], extending
1269 /// the lifetime of the value if successful.
1271 /// Returns [`None`] if the value has since been dropped.
1273 /// [`Rc`]: struct.Rc.html
1274 /// [`None`]: ../../std/option/enum.Option.html
1279 /// use std::rc::Rc;
1281 /// let five = Rc::new(5);
1283 /// let weak_five = Rc::downgrade(&five);
1285 /// let strong_five: Option<Rc<_>> = weak_five.upgrade();
1286 /// assert!(strong_five.is_some());
1288 /// // Destroy all strong pointers.
1289 /// drop(strong_five);
1292 /// assert!(weak_five.upgrade().is_none());
1294 #[stable(feature = "rc_weak", since = "1.4.0")]
1295 pub fn upgrade(&self) -> Option<Rc<T>> {
1296 let inner = self.inner()?;
1297 if inner.strong() == 0 {
1301 Some(Rc { ptr: self.ptr, phantom: PhantomData })
1305 /// Gets the number of strong (`Rc`) pointers pointing to this value.
1307 /// If `self` was created using [`Weak::new`], this will return 0.
1309 /// [`Weak::new`]: #method.new
1310 #[unstable(feature = "weak_counts", issue = "57977")]
1311 pub fn strong_count(&self) -> usize {
1312 if let Some(inner) = self.inner() {
1319 /// Gets the number of `Weak` pointers pointing to this value.
1321 /// If `self` was created using [`Weak::new`], this will return `None`. If
1322 /// not, the returned value is at least 1, since `self` still points to the
1325 /// [`Weak::new`]: #method.new
1326 #[unstable(feature = "weak_counts", issue = "57977")]
1327 pub fn weak_count(&self) -> Option<usize> {
1328 self.inner().map(|inner| {
1329 if inner.strong() > 0 {
1330 inner.weak() - 1 // subtract the implicit weak ptr
1337 /// Return `None` when the pointer is dangling and there is no allocated `RcBox`,
1338 /// i.e., this `Weak` was created by `Weak::new`
1340 fn inner(&self) -> Option<&RcBox<T>> {
1341 if is_dangling(self.ptr) {
1344 Some(unsafe { self.ptr.as_ref() })
1348 /// Returns true if the two `Weak`s point to the same value (not just values
1349 /// that compare as equal).
1353 /// Since this compares pointers it means that `Weak::new()` will equal each
1354 /// other, even though they don't point to any value.
1359 /// #![feature(weak_ptr_eq)]
1360 /// use std::rc::{Rc, Weak};
1362 /// let first_rc = Rc::new(5);
1363 /// let first = Rc::downgrade(&first_rc);
1364 /// let second = Rc::downgrade(&first_rc);
1366 /// assert!(Weak::ptr_eq(&first, &second));
1368 /// let third_rc = Rc::new(5);
1369 /// let third = Rc::downgrade(&third_rc);
1371 /// assert!(!Weak::ptr_eq(&first, &third));
1374 /// Comparing `Weak::new`.
1377 /// #![feature(weak_ptr_eq)]
1378 /// use std::rc::{Rc, Weak};
1380 /// let first = Weak::new();
1381 /// let second = Weak::new();
1382 /// assert!(Weak::ptr_eq(&first, &second));
1384 /// let third_rc = Rc::new(());
1385 /// let third = Rc::downgrade(&third_rc);
1386 /// assert!(!Weak::ptr_eq(&first, &third));
1389 #[unstable(feature = "weak_ptr_eq", issue = "55981")]
1390 pub fn ptr_eq(this: &Self, other: &Self) -> bool {
1391 this.ptr.as_ptr() == other.ptr.as_ptr()
1395 #[stable(feature = "rc_weak", since = "1.4.0")]
1396 impl<T: ?Sized> Drop for Weak<T> {
1397 /// Drops the `Weak` pointer.
1402 /// use std::rc::{Rc, Weak};
1406 /// impl Drop for Foo {
1407 /// fn drop(&mut self) {
1408 /// println!("dropped!");
1412 /// let foo = Rc::new(Foo);
1413 /// let weak_foo = Rc::downgrade(&foo);
1414 /// let other_weak_foo = Weak::clone(&weak_foo);
1416 /// drop(weak_foo); // Doesn't print anything
1417 /// drop(foo); // Prints "dropped!"
1419 /// assert!(other_weak_foo.upgrade().is_none());
1421 fn drop(&mut self) {
1422 if let Some(inner) = self.inner() {
1424 // the weak count starts at 1, and will only go to zero if all
1425 // the strong pointers have disappeared.
1426 if inner.weak() == 0 {
1428 Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref()));
1435 #[stable(feature = "rc_weak", since = "1.4.0")]
1436 impl<T: ?Sized> Clone for Weak<T> {
1437 /// Makes a clone of the `Weak` pointer that points to the same value.
1442 /// use std::rc::{Rc, Weak};
1444 /// let weak_five = Rc::downgrade(&Rc::new(5));
1446 /// let _ = Weak::clone(&weak_five);
1449 fn clone(&self) -> Weak<T> {
1450 if let Some(inner) = self.inner() {
1453 Weak { ptr: self.ptr }
1457 #[stable(feature = "rc_weak", since = "1.4.0")]
1458 impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> {
1459 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1464 #[stable(feature = "downgraded_weak", since = "1.10.0")]
1465 impl<T> Default for Weak<T> {
1466 /// Constructs a new `Weak<T>`, allocating memory for `T` without initializing
1467 /// it. Calling [`upgrade`] on the return value always gives [`None`].
1469 /// [`None`]: ../../std/option/enum.Option.html
1470 /// [`upgrade`]: ../../std/rc/struct.Weak.html#method.upgrade
1475 /// use std::rc::Weak;
1477 /// let empty: Weak<i64> = Default::default();
1478 /// assert!(empty.upgrade().is_none());
1480 fn default() -> Weak<T> {
1485 // NOTE: We checked_add here to deal with mem::forget safely. In particular
1486 // if you mem::forget Rcs (or Weaks), the ref-count can overflow, and then
1487 // you can free the allocation while outstanding Rcs (or Weaks) exist.
1488 // We abort because this is such a degenerate scenario that we don't care about
1489 // what happens -- no real program should ever experience this.
1491 // This should have negligible overhead since you don't actually need to
1492 // clone these much in Rust thanks to ownership and move-semantics.
1495 trait RcBoxPtr<T: ?Sized> {
1496 fn inner(&self) -> &RcBox<T>;
1499 fn strong(&self) -> usize {
1500 self.inner().strong.get()
1504 fn inc_strong(&self) {
1505 // We want to abort on overflow instead of dropping the value.
1506 // The reference count will never be zero when this is called;
1507 // nevertheless, we insert an abort here to hint LLVM at
1508 // an otherwise missed optimization.
1509 if self.strong() == 0 || self.strong() == usize::max_value() {
1512 self.inner().strong.set(self.strong() + 1);
1516 fn dec_strong(&self) {
1517 self.inner().strong.set(self.strong() - 1);
1521 fn weak(&self) -> usize {
1522 self.inner().weak.get()
1526 fn inc_weak(&self) {
1527 // We want to abort on overflow instead of dropping the value.
1528 // The reference count will never be zero when this is called;
1529 // nevertheless, we insert an abort here to hint LLVM at
1530 // an otherwise missed optimization.
1531 if self.weak() == 0 || self.weak() == usize::max_value() {
1534 self.inner().weak.set(self.weak() + 1);
1538 fn dec_weak(&self) {
1539 self.inner().weak.set(self.weak() - 1);
1543 impl<T: ?Sized> RcBoxPtr<T> for Rc<T> {
1545 fn inner(&self) -> &RcBox<T> {
1552 impl<T: ?Sized> RcBoxPtr<T> for RcBox<T> {
1554 fn inner(&self) -> &RcBox<T> {
1561 use super::{Rc, Weak};
1562 use std::boxed::Box;
1563 use std::cell::RefCell;
1564 use std::option::Option::{self, None, Some};
1565 use std::result::Result::{Err, Ok};
1567 use std::clone::Clone;
1568 use std::convert::From;
1572 let x = Rc::new(RefCell::new(5));
1574 *x.borrow_mut() = 20;
1575 assert_eq!(*y.borrow(), 20);
1585 fn test_simple_clone() {
1593 fn test_destructor() {
1594 let x: Rc<Box<_>> = Rc::new(box 5);
1601 let y = Rc::downgrade(&x);
1602 assert!(y.upgrade().is_some());
1608 let y = Rc::downgrade(&x);
1610 assert!(y.upgrade().is_none());
1614 fn weak_self_cyclic() {
1616 x: RefCell<Option<Weak<Cycle>>>,
1619 let a = Rc::new(Cycle { x: RefCell::new(None) });
1620 let b = Rc::downgrade(&a.clone());
1621 *a.x.borrow_mut() = Some(b);
1623 // hopefully we don't double-free (or leak)...
1629 assert!(Rc::is_unique(&x));
1631 assert!(!Rc::is_unique(&x));
1633 assert!(Rc::is_unique(&x));
1634 let w = Rc::downgrade(&x);
1635 assert!(!Rc::is_unique(&x));
1637 assert!(Rc::is_unique(&x));
1641 fn test_strong_count() {
1643 assert!(Rc::strong_count(&a) == 1);
1644 let w = Rc::downgrade(&a);
1645 assert!(Rc::strong_count(&a) == 1);
1646 let b = w.upgrade().expect("upgrade of live rc failed");
1647 assert!(Rc::strong_count(&b) == 2);
1648 assert!(Rc::strong_count(&a) == 2);
1651 assert!(Rc::strong_count(&b) == 1);
1653 assert!(Rc::strong_count(&b) == 2);
1654 assert!(Rc::strong_count(&c) == 2);
1658 fn test_weak_count() {
1660 assert!(Rc::strong_count(&a) == 1);
1661 assert!(Rc::weak_count(&a) == 0);
1662 let w = Rc::downgrade(&a);
1663 assert!(Rc::strong_count(&a) == 1);
1664 assert!(Rc::weak_count(&a) == 1);
1666 assert!(Rc::strong_count(&a) == 1);
1667 assert!(Rc::weak_count(&a) == 0);
1669 assert!(Rc::strong_count(&a) == 2);
1670 assert!(Rc::weak_count(&a) == 0);
1676 assert_eq!(Weak::weak_count(&Weak::<u64>::new()), None);
1677 assert_eq!(Weak::strong_count(&Weak::<u64>::new()), 0);
1680 let w = Rc::downgrade(&a);
1681 assert_eq!(Weak::strong_count(&w), 1);
1682 assert_eq!(Weak::weak_count(&w), Some(1));
1684 assert_eq!(Weak::strong_count(&w), 1);
1685 assert_eq!(Weak::weak_count(&w), Some(2));
1686 assert_eq!(Weak::strong_count(&w2), 1);
1687 assert_eq!(Weak::weak_count(&w2), Some(2));
1689 assert_eq!(Weak::strong_count(&w2), 1);
1690 assert_eq!(Weak::weak_count(&w2), Some(1));
1692 assert_eq!(Weak::strong_count(&w2), 2);
1693 assert_eq!(Weak::weak_count(&w2), Some(1));
1696 assert_eq!(Weak::strong_count(&w2), 0);
1697 assert_eq!(Weak::weak_count(&w2), Some(1));
1704 assert_eq!(Rc::try_unwrap(x), Ok(3));
1707 assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4)));
1709 let _w = Rc::downgrade(&x);
1710 assert_eq!(Rc::try_unwrap(x), Ok(5));
1714 fn into_from_raw() {
1715 let x = Rc::new(box "hello");
1718 let x_ptr = Rc::into_raw(x);
1721 assert_eq!(**x_ptr, "hello");
1723 let x = Rc::from_raw(x_ptr);
1724 assert_eq!(**x, "hello");
1726 assert_eq!(Rc::try_unwrap(x).map(|x| *x), Ok("hello"));
1731 fn test_into_from_raw_unsized() {
1732 use std::fmt::Display;
1733 use std::string::ToString;
1735 let rc: Rc<str> = Rc::from("foo");
1737 let ptr = Rc::into_raw(rc.clone());
1738 let rc2 = unsafe { Rc::from_raw(ptr) };
1740 assert_eq!(unsafe { &*ptr }, "foo");
1741 assert_eq!(rc, rc2);
1743 let rc: Rc<dyn Display> = Rc::new(123);
1745 let ptr = Rc::into_raw(rc.clone());
1746 let rc2 = unsafe { Rc::from_raw(ptr) };
1748 assert_eq!(unsafe { &*ptr }.to_string(), "123");
1749 assert_eq!(rc2.to_string(), "123");
1754 let mut x = Rc::new(3);
1755 *Rc::get_mut(&mut x).unwrap() = 4;
1758 assert!(Rc::get_mut(&mut x).is_none());
1760 assert!(Rc::get_mut(&mut x).is_some());
1761 let _w = Rc::downgrade(&x);
1762 assert!(Rc::get_mut(&mut x).is_none());
1766 fn test_cowrc_clone_make_unique() {
1767 let mut cow0 = Rc::new(75);
1768 let mut cow1 = cow0.clone();
1769 let mut cow2 = cow1.clone();
1771 assert!(75 == *Rc::make_mut(&mut cow0));
1772 assert!(75 == *Rc::make_mut(&mut cow1));
1773 assert!(75 == *Rc::make_mut(&mut cow2));
1775 *Rc::make_mut(&mut cow0) += 1;
1776 *Rc::make_mut(&mut cow1) += 2;
1777 *Rc::make_mut(&mut cow2) += 3;
1779 assert!(76 == *cow0);
1780 assert!(77 == *cow1);
1781 assert!(78 == *cow2);
1783 // none should point to the same backing memory
1784 assert!(*cow0 != *cow1);
1785 assert!(*cow0 != *cow2);
1786 assert!(*cow1 != *cow2);
1790 fn test_cowrc_clone_unique2() {
1791 let mut cow0 = Rc::new(75);
1792 let cow1 = cow0.clone();
1793 let cow2 = cow1.clone();
1795 assert!(75 == *cow0);
1796 assert!(75 == *cow1);
1797 assert!(75 == *cow2);
1799 *Rc::make_mut(&mut cow0) += 1;
1801 assert!(76 == *cow0);
1802 assert!(75 == *cow1);
1803 assert!(75 == *cow2);
1805 // cow1 and cow2 should share the same contents
1806 // cow0 should have a unique reference
1807 assert!(*cow0 != *cow1);
1808 assert!(*cow0 != *cow2);
1809 assert!(*cow1 == *cow2);
1813 fn test_cowrc_clone_weak() {
1814 let mut cow0 = Rc::new(75);
1815 let cow1_weak = Rc::downgrade(&cow0);
1817 assert!(75 == *cow0);
1818 assert!(75 == *cow1_weak.upgrade().unwrap());
1820 *Rc::make_mut(&mut cow0) += 1;
1822 assert!(76 == *cow0);
1823 assert!(cow1_weak.upgrade().is_none());
1828 let foo = Rc::new(75);
1829 assert_eq!(format!("{:?}", foo), "75");
1834 let foo: Rc<[i32]> = Rc::new([1, 2, 3]);
1835 assert_eq!(foo, foo.clone());
1839 fn test_from_owned() {
1841 let foo_rc = Rc::from(foo);
1842 assert!(123 == *foo_rc);
1846 fn test_new_weak() {
1847 let foo: Weak<usize> = Weak::new();
1848 assert!(foo.upgrade().is_none());
1853 let five = Rc::new(5);
1854 let same_five = five.clone();
1855 let other_five = Rc::new(5);
1857 assert!(Rc::ptr_eq(&five, &same_five));
1858 assert!(!Rc::ptr_eq(&five, &other_five));
1862 fn test_from_str() {
1863 let r: Rc<str> = Rc::from("foo");
1865 assert_eq!(&r[..], "foo");
1869 fn test_copy_from_slice() {
1870 let s: &[u32] = &[1, 2, 3];
1871 let r: Rc<[u32]> = Rc::from(s);
1873 assert_eq!(&r[..], [1, 2, 3]);
1877 fn test_clone_from_slice() {
1878 #[derive(Clone, Debug, Eq, PartialEq)]
1881 let s: &[X] = &[X(1), X(2), X(3)];
1882 let r: Rc<[X]> = Rc::from(s);
1884 assert_eq!(&r[..], s);
1889 fn test_clone_from_slice_panic() {
1890 use std::string::{String, ToString};
1892 struct Fail(u32, String);
1894 impl Clone for Fail {
1895 fn clone(&self) -> Fail {
1899 Fail(self.0, self.1.clone())
1904 Fail(0, "foo".to_string()),
1905 Fail(1, "bar".to_string()),
1906 Fail(2, "baz".to_string()),
1909 // Should panic, but not cause memory corruption
1910 let _r: Rc<[Fail]> = Rc::from(s);
1914 fn test_from_box() {
1915 let b: Box<u32> = box 123;
1916 let r: Rc<u32> = Rc::from(b);
1918 assert_eq!(*r, 123);
1922 fn test_from_box_str() {
1923 use std::string::String;
1925 let s = String::from("foo").into_boxed_str();
1926 let r: Rc<str> = Rc::from(s);
1928 assert_eq!(&r[..], "foo");
1932 fn test_from_box_slice() {
1933 let s = vec![1, 2, 3].into_boxed_slice();
1934 let r: Rc<[u32]> = Rc::from(s);
1936 assert_eq!(&r[..], [1, 2, 3]);
1940 fn test_from_box_trait() {
1941 use std::fmt::Display;
1942 use std::string::ToString;
1944 let b: Box<dyn Display> = box 123;
1945 let r: Rc<dyn Display> = Rc::from(b);
1947 assert_eq!(r.to_string(), "123");
1951 fn test_from_box_trait_zero_sized() {
1952 use std::fmt::Debug;
1954 let b: Box<dyn Debug> = box ();
1955 let r: Rc<dyn Debug> = Rc::from(b);
1957 assert_eq!(format!("{:?}", r), "()");
1961 fn test_from_vec() {
1962 let v = vec![1, 2, 3];
1963 let r: Rc<[u32]> = Rc::from(v);
1965 assert_eq!(&r[..], [1, 2, 3]);
1969 fn test_downcast() {
1972 let r1: Rc<dyn Any> = Rc::new(i32::max_value());
1973 let r2: Rc<dyn Any> = Rc::new("abc");
1975 assert!(r1.clone().downcast::<u32>().is_err());
1977 let r1i32 = r1.downcast::<i32>();
1978 assert!(r1i32.is_ok());
1979 assert_eq!(r1i32.unwrap(), Rc::new(i32::max_value()));
1981 assert!(r2.clone().downcast::<i32>().is_err());
1983 let r2str = r2.downcast::<&'static str>();
1984 assert!(r2str.is_ok());
1985 assert_eq!(r2str.unwrap(), Rc::new("abc"));
1989 #[stable(feature = "rust1", since = "1.0.0")]
1990 impl<T: ?Sized> borrow::Borrow<T> for Rc<T> {
1991 fn borrow(&self) -> &T {
1996 #[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
1997 impl<T: ?Sized> AsRef<T> for Rc<T> {
1998 fn as_ref(&self) -> &T {
2003 #[stable(feature = "pin", since = "1.33.0")]
2004 impl<T: ?Sized> Unpin for Rc<T> { }