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Diffstat (limited to 'src/liballoc/rc.rs')
| -rw-r--r-- | src/liballoc/rc.rs | 2138 |
1 files changed, 0 insertions, 2138 deletions
diff --git a/src/liballoc/rc.rs b/src/liballoc/rc.rs deleted file mode 100644 index 96dfc2f4251..00000000000 --- a/src/liballoc/rc.rs +++ /dev/null @@ -1,2138 +0,0 @@ -//! Single-threaded reference-counting pointers. 'Rc' stands for 'Reference -//! Counted'. -//! -//! The type [`Rc<T>`][`Rc`] provides shared ownership of a value of type `T`, -//! allocated in the heap. Invoking [`clone`][clone] on [`Rc`] produces a new -//! pointer to the same allocation in the heap. When the last [`Rc`] pointer to a -//! given allocation is destroyed, the value stored in that allocation (often -//! referred to as "inner value") is also dropped. -//! -//! Shared references in Rust disallow mutation by default, and [`Rc`] -//! is no exception: you cannot generally obtain a mutable reference to -//! something inside an [`Rc`]. If you need mutability, put a [`Cell`] -//! or [`RefCell`] inside the [`Rc`]; see [an example of mutability -//! inside an Rc][mutability]. -//! -//! [`Rc`] uses non-atomic reference counting. This means that overhead is very -//! low, but an [`Rc`] cannot be sent between threads, and consequently [`Rc`] -//! does not implement [`Send`][send]. As a result, the Rust compiler -//! will check *at compile time* that you are not sending [`Rc`]s between -//! threads. If you need multi-threaded, atomic reference counting, use -//! [`sync::Arc`][arc]. -//! -//! The [`downgrade`][downgrade] method can be used to create a non-owning -//! [`Weak`] pointer. A [`Weak`] pointer can be [`upgrade`][upgrade]d -//! to an [`Rc`], but this will return [`None`] if the value stored in the allocation has -//! already been dropped. In other words, `Weak` pointers do not keep the value -//! inside the allocation alive; however, they *do* keep the allocation -//! (the backing store for the inner value) alive. -//! -//! A cycle between [`Rc`] pointers will never be deallocated. For this reason, -//! [`Weak`] is used to break cycles. For example, a tree could have strong -//! [`Rc`] pointers from parent nodes to children, and [`Weak`] pointers from -//! children back to their parents. -//! -//! `Rc<T>` automatically dereferences to `T` (via the [`Deref`] trait), -//! so you can call `T`'s methods on a value of type [`Rc<T>`][`Rc`]. To avoid name -//! clashes with `T`'s methods, the methods of [`Rc<T>`][`Rc`] itself are associated -//! functions, called using function-like syntax: -//! -//! ``` -//! use std::rc::Rc; -//! let my_rc = Rc::new(()); -//! -//! Rc::downgrade(&my_rc); -//! ``` -//! -//! [`Weak<T>`][`Weak`] does not auto-dereference to `T`, because the inner value may have -//! already been dropped. -//! -//! # Cloning references -//! -//! Creating a new reference to the same allocation as an existing reference counted pointer -//! is done using the `Clone` trait implemented for [`Rc<T>`][`Rc`] and [`Weak<T>`][`Weak`]. -//! -//! ``` -//! use std::rc::Rc; -//! let foo = Rc::new(vec![1.0, 2.0, 3.0]); -//! // The two syntaxes below are equivalent. -//! let a = foo.clone(); -//! let b = Rc::clone(&foo); -//! // a and b both point to the same memory location as foo. -//! ``` -//! -//! The `Rc::clone(&from)` syntax is the most idiomatic because it conveys more explicitly -//! the meaning of the code. In the example above, this syntax makes it easier to see that -//! this code is creating a new reference rather than copying the whole content of foo. -//! -//! # Examples -//! -//! Consider a scenario where a set of `Gadget`s are owned by a given `Owner`. -//! We want to have our `Gadget`s point to their `Owner`. We can't do this with -//! unique ownership, because more than one gadget may belong to the same -//! `Owner`. [`Rc`] allows us to share an `Owner` between multiple `Gadget`s, -//! and have the `Owner` remain allocated as long as any `Gadget` points at it. -//! -//! ``` -//! use std::rc::Rc; -//! -//! struct Owner { -//! name: String, -//! // ...other fields -//! } -//! -//! struct Gadget { -//! id: i32, -//! owner: Rc<Owner>, -//! // ...other fields -//! } -//! -//! fn main() { -//! // Create a reference-counted `Owner`. -//! let gadget_owner: Rc<Owner> = Rc::new( -//! Owner { -//! name: "Gadget Man".to_string(), -//! } -//! ); -//! -//! // Create `Gadget`s belonging to `gadget_owner`. Cloning the `Rc<Owner>` -//! // gives us a new pointer to the same `Owner` allocation, incrementing -//! // the reference count in the process. -//! let gadget1 = Gadget { -//! id: 1, -//! owner: Rc::clone(&gadget_owner), -//! }; -//! let gadget2 = Gadget { -//! id: 2, -//! owner: Rc::clone(&gadget_owner), -//! }; -//! -//! // Dispose of our local variable `gadget_owner`. -//! drop(gadget_owner); -//! -//! // Despite dropping `gadget_owner`, we're still able to print out the name -//! // of the `Owner` of the `Gadget`s. This is because we've only dropped a -//! // single `Rc<Owner>`, not the `Owner` it points to. As long as there are -//! // other `Rc<Owner>` pointing at the same `Owner` allocation, it will remain -//! // live. The field projection `gadget1.owner.name` works because -//! // `Rc<Owner>` automatically dereferences to `Owner`. -//! println!("Gadget {} owned by {}", gadget1.id, gadget1.owner.name); -//! println!("Gadget {} owned by {}", gadget2.id, gadget2.owner.name); -//! -//! // At the end of the function, `gadget1` and `gadget2` are destroyed, and -//! // with them the last counted references to our `Owner`. Gadget Man now -//! // gets destroyed as well. -//! } -//! ``` -//! -//! If our requirements change, and we also need to be able to traverse from -//! `Owner` to `Gadget`, we will run into problems. An [`Rc`] pointer from `Owner` -//! to `Gadget` introduces a cycle. This means that their -//! reference counts can never reach 0, and the allocation will never be destroyed: -//! a memory leak. In order to get around this, we can use [`Weak`] -//! pointers. -//! -//! Rust actually makes it somewhat difficult to produce this loop in the first -//! place. In order to end up with two values that point at each other, one of -//! them needs to be mutable. This is difficult because [`Rc`] enforces -//! memory safety by only giving out shared references to the value it wraps, -//! and these don't allow direct mutation. We need to wrap the part of the -//! value we wish to mutate in a [`RefCell`], which provides *interior -//! mutability*: a method to achieve mutability through a shared reference. -//! [`RefCell`] enforces Rust's borrowing rules at runtime. -//! -//! ``` -//! use std::rc::Rc; -//! use std::rc::Weak; -//! use std::cell::RefCell; -//! -//! struct Owner { -//! name: String, -//! gadgets: RefCell<Vec<Weak<Gadget>>>, -//! // ...other fields -//! } -//! -//! struct Gadget { -//! id: i32, -//! owner: Rc<Owner>, -//! // ...other fields -//! } -//! -//! fn main() { -//! // Create a reference-counted `Owner`. Note that we've put the `Owner`'s -//! // vector of `Gadget`s inside a `RefCell` so that we can mutate it through -//! // a shared reference. -//! let gadget_owner: Rc<Owner> = Rc::new( -//! Owner { -//! name: "Gadget Man".to_string(), -//! gadgets: RefCell::new(vec![]), -//! } -//! ); -//! -//! // Create `Gadget`s belonging to `gadget_owner`, as before. -//! let gadget1 = Rc::new( -//! Gadget { -//! id: 1, -//! owner: Rc::clone(&gadget_owner), -//! } -//! ); -//! let gadget2 = Rc::new( -//! Gadget { -//! id: 2, -//! owner: Rc::clone(&gadget_owner), -//! } -//! ); -//! -//! // Add the `Gadget`s to their `Owner`. -//! { -//! let mut gadgets = gadget_owner.gadgets.borrow_mut(); -//! gadgets.push(Rc::downgrade(&gadget1)); -//! gadgets.push(Rc::downgrade(&gadget2)); -//! -//! // `RefCell` dynamic borrow ends here. -//! } -//! -//! // Iterate over our `Gadget`s, printing their details out. -//! for gadget_weak in gadget_owner.gadgets.borrow().iter() { -//! -//! // `gadget_weak` is a `Weak<Gadget>`. Since `Weak` pointers can't -//! // guarantee the allocation still exists, we need to call -//! // `upgrade`, which returns an `Option<Rc<Gadget>>`. -//! // -//! // In this case we know the allocation still exists, so we simply -//! // `unwrap` the `Option`. In a more complicated program, you might -//! // need graceful error handling for a `None` result. -//! -//! let gadget = gadget_weak.upgrade().unwrap(); -//! println!("Gadget {} owned by {}", gadget.id, gadget.owner.name); -//! } -//! -//! // At the end of the function, `gadget_owner`, `gadget1`, and `gadget2` -//! // are destroyed. There are now no strong (`Rc`) pointers to the -//! // gadgets, so they are destroyed. This zeroes the reference count on -//! // Gadget Man, so he gets destroyed as well. -//! } -//! ``` -//! -//! [`Rc`]: struct.Rc.html -//! [`Weak`]: struct.Weak.html -//! [clone]: ../../std/clone/trait.Clone.html#tymethod.clone -//! [`Cell`]: ../../std/cell/struct.Cell.html -//! [`RefCell`]: ../../std/cell/struct.RefCell.html -//! [send]: ../../std/marker/trait.Send.html -//! [arc]: ../../std/sync/struct.Arc.html -//! [`Deref`]: ../../std/ops/trait.Deref.html -//! [downgrade]: struct.Rc.html#method.downgrade -//! [upgrade]: struct.Weak.html#method.upgrade -//! [`None`]: ../../std/option/enum.Option.html#variant.None -//! [mutability]: ../../std/cell/index.html#introducing-mutability-inside-of-something-immutable - -#![stable(feature = "rust1", since = "1.0.0")] - -#[cfg(not(test))] -use crate::boxed::Box; -#[cfg(test)] -use std::boxed::Box; - -use core::any::Any; -use core::borrow; -use core::cell::Cell; -use core::cmp::Ordering; -use core::convert::{From, TryFrom}; -use core::fmt; -use core::hash::{Hash, Hasher}; -use core::intrinsics::abort; -use core::iter; -use core::marker::{self, PhantomData, Unpin, Unsize}; -use core::mem::{self, align_of_val_raw, forget, size_of_val}; -use core::ops::{CoerceUnsized, Deref, DispatchFromDyn, Receiver}; -use core::pin::Pin; -use core::ptr::{self, NonNull}; -use core::slice::from_raw_parts_mut; - -use crate::alloc::{box_free, handle_alloc_error, AllocInit, AllocRef, Global, Layout}; -use crate::borrow::{Cow, ToOwned}; -use crate::string::String; -use crate::vec::Vec; - -#[cfg(test)] -mod tests; - -// This is repr(C) to future-proof against possible field-reordering, which -// would interfere with otherwise safe [into|from]_raw() of transmutable -// inner types. -#[repr(C)] -struct RcBox<T: ?Sized> { - strong: Cell<usize>, - weak: Cell<usize>, - value: T, -} - -/// A single-threaded reference-counting pointer. 'Rc' stands for 'Reference -/// Counted'. -/// -/// See the [module-level documentation](./index.html) for more details. -/// -/// The inherent methods of `Rc` are all associated functions, which means -/// that you have to call them as e.g., [`Rc::get_mut(&mut value)`][get_mut] instead of -/// `value.get_mut()`. This avoids conflicts with methods of the inner -/// type `T`. -/// -/// [get_mut]: #method.get_mut -#[cfg_attr(not(test), rustc_diagnostic_item = "Rc")] -#[stable(feature = "rust1", since = "1.0.0")] -pub struct Rc<T: ?Sized> { - ptr: NonNull<RcBox<T>>, - phantom: PhantomData<RcBox<T>>, -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl<T: ?Sized> !marker::Send for Rc<T> {} -#[stable(feature = "rust1", since = "1.0.0")] -impl<T: ?Sized> !marker::Sync for Rc<T> {} - -#[unstable(feature = "coerce_unsized", issue = "27732")] -impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Rc<U>> for Rc<T> {} - -#[unstable(feature = "dispatch_from_dyn", issue = "none")] -impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Rc<U>> for Rc<T> {} - -impl<T: ?Sized> Rc<T> { - fn from_inner(ptr: NonNull<RcBox<T>>) -> Self { - Self { ptr, phantom: PhantomData } - } - - unsafe fn from_ptr(ptr: *mut RcBox<T>) -> Self { - Self::from_inner(unsafe { NonNull::new_unchecked(ptr) }) - } -} - -impl<T> Rc<T> { - /// Constructs a new `Rc<T>`. - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let five = Rc::new(5); - /// ``` - #[stable(feature = "rust1", since = "1.0.0")] - pub fn new(value: T) -> Rc<T> { - // There is an implicit weak pointer owned by all the strong - // pointers, which ensures that the weak destructor never frees - // the allocation while the strong destructor is running, even - // if the weak pointer is stored inside the strong one. - Self::from_inner( - Box::leak(box RcBox { strong: Cell::new(1), weak: Cell::new(1), value }).into(), - ) - } - - /// Constructs a new `Rc` with uninitialized contents. - /// - /// # Examples - /// - /// ``` - /// #![feature(new_uninit)] - /// #![feature(get_mut_unchecked)] - /// - /// use std::rc::Rc; - /// - /// let mut five = Rc::<u32>::new_uninit(); - /// - /// let five = unsafe { - /// // Deferred initialization: - /// Rc::get_mut_unchecked(&mut five).as_mut_ptr().write(5); - /// - /// five.assume_init() - /// }; - /// - /// assert_eq!(*five, 5) - /// ``` - #[unstable(feature = "new_uninit", issue = "63291")] - pub fn new_uninit() -> Rc<mem::MaybeUninit<T>> { - unsafe { - Rc::from_ptr(Rc::allocate_for_layout(Layout::new::<T>(), |mem| { - mem as *mut RcBox<mem::MaybeUninit<T>> - })) - } - } - - /// Constructs a new `Rc` with uninitialized contents, with the memory - /// being filled with `0` bytes. - /// - /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and - /// incorrect usage of this method. - /// - /// # Examples - /// - /// ``` - /// #![feature(new_uninit)] - /// - /// use std::rc::Rc; - /// - /// let zero = Rc::<u32>::new_zeroed(); - /// let zero = unsafe { zero.assume_init() }; - /// - /// assert_eq!(*zero, 0) - /// ``` - /// - /// [zeroed]: ../../std/mem/union.MaybeUninit.html#method.zeroed - #[unstable(feature = "new_uninit", issue = "63291")] - pub fn new_zeroed() -> Rc<mem::MaybeUninit<T>> { - unsafe { - let mut uninit = Self::new_uninit(); - ptr::write_bytes::<T>(Rc::get_mut_unchecked(&mut uninit).as_mut_ptr(), 0, 1); - uninit - } - } - - /// Constructs a new `Pin<Rc<T>>`. If `T` does not implement `Unpin`, then - /// `value` will be pinned in memory and unable to be moved. - #[stable(feature = "pin", since = "1.33.0")] - pub fn pin(value: T) -> Pin<Rc<T>> { - unsafe { Pin::new_unchecked(Rc::new(value)) } - } - - /// Returns the inner value, if the `Rc` has exactly one strong reference. - /// - /// Otherwise, an [`Err`][result] is returned with the same `Rc` that was - /// passed in. - /// - /// This will succeed even if there are outstanding weak references. - /// - /// [result]: ../../std/result/enum.Result.html - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let x = Rc::new(3); - /// assert_eq!(Rc::try_unwrap(x), Ok(3)); - /// - /// let x = Rc::new(4); - /// let _y = Rc::clone(&x); - /// assert_eq!(*Rc::try_unwrap(x).unwrap_err(), 4); - /// ``` - #[inline] - #[stable(feature = "rc_unique", since = "1.4.0")] - pub fn try_unwrap(this: Self) -> Result<T, Self> { - if Rc::strong_count(&this) == 1 { - unsafe { - let val = ptr::read(&*this); // copy the contained object - - // Indicate to Weaks that they can't be promoted by decrementing - // the strong count, and then remove the implicit "strong weak" - // pointer while also handling drop logic by just crafting a - // fake Weak. - this.dec_strong(); - let _weak = Weak { ptr: this.ptr }; - forget(this); - Ok(val) - } - } else { - Err(this) - } - } -} - -impl<T> Rc<[T]> { - /// Constructs a new reference-counted slice with uninitialized contents. - /// - /// # Examples - /// - /// ``` - /// #![feature(new_uninit)] - /// #![feature(get_mut_unchecked)] - /// - /// use std::rc::Rc; - /// - /// let mut values = Rc::<[u32]>::new_uninit_slice(3); - /// - /// let values = unsafe { - /// // Deferred initialization: - /// Rc::get_mut_unchecked(&mut values)[0].as_mut_ptr().write(1); - /// Rc::get_mut_unchecked(&mut values)[1].as_mut_ptr().write(2); - /// Rc::get_mut_unchecked(&mut values)[2].as_mut_ptr().write(3); - /// - /// values.assume_init() - /// }; - /// - /// assert_eq!(*values, [1, 2, 3]) - /// ``` - #[unstable(feature = "new_uninit", issue = "63291")] - pub fn new_uninit_slice(len: usize) -> Rc<[mem::MaybeUninit<T>]> { - unsafe { Rc::from_ptr(Rc::allocate_for_slice(len)) } - } -} - -impl<T> Rc<mem::MaybeUninit<T>> { - /// Converts to `Rc<T>`. - /// - /// # Safety - /// - /// As with [`MaybeUninit::assume_init`], - /// it is up to the caller to guarantee that the inner value - /// really is in an initialized state. - /// Calling this when the content is not yet fully initialized - /// causes immediate undefined behavior. - /// - /// [`MaybeUninit::assume_init`]: ../../std/mem/union.MaybeUninit.html#method.assume_init - /// - /// # Examples - /// - /// ``` - /// #![feature(new_uninit)] - /// #![feature(get_mut_unchecked)] - /// - /// use std::rc::Rc; - /// - /// let mut five = Rc::<u32>::new_uninit(); - /// - /// let five = unsafe { - /// // Deferred initialization: - /// Rc::get_mut_unchecked(&mut five).as_mut_ptr().write(5); - /// - /// five.assume_init() - /// }; - /// - /// assert_eq!(*five, 5) - /// ``` - #[unstable(feature = "new_uninit", issue = "63291")] - #[inline] - pub unsafe fn assume_init(self) -> Rc<T> { - Rc::from_inner(mem::ManuallyDrop::new(self).ptr.cast()) - } -} - -impl<T> Rc<[mem::MaybeUninit<T>]> { - /// Converts to `Rc<[T]>`. - /// - /// # Safety - /// - /// As with [`MaybeUninit::assume_init`], - /// it is up to the caller to guarantee that the inner value - /// really is in an initialized state. - /// Calling this when the content is not yet fully initialized - /// causes immediate undefined behavior. - /// - /// [`MaybeUninit::assume_init`]: ../../std/mem/union.MaybeUninit.html#method.assume_init - /// - /// # Examples - /// - /// ``` - /// #![feature(new_uninit)] - /// #![feature(get_mut_unchecked)] - /// - /// use std::rc::Rc; - /// - /// let mut values = Rc::<[u32]>::new_uninit_slice(3); - /// - /// let values = unsafe { - /// // Deferred initialization: - /// Rc::get_mut_unchecked(&mut values)[0].as_mut_ptr().write(1); - /// Rc::get_mut_unchecked(&mut values)[1].as_mut_ptr().write(2); - /// Rc::get_mut_unchecked(&mut values)[2].as_mut_ptr().write(3); - /// - /// values.assume_init() - /// }; - /// - /// assert_eq!(*values, [1, 2, 3]) - /// ``` - #[unstable(feature = "new_uninit", issue = "63291")] - #[inline] - pub unsafe fn assume_init(self) -> Rc<[T]> { - unsafe { Rc::from_ptr(mem::ManuallyDrop::new(self).ptr.as_ptr() as _) } - } -} - -impl<T: ?Sized> Rc<T> { - /// Consumes the `Rc`, returning the wrapped pointer. - /// - /// To avoid a memory leak the pointer must be converted back to an `Rc` using - /// [`Rc::from_raw`][from_raw]. - /// - /// [from_raw]: struct.Rc.html#method.from_raw - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let x = Rc::new("hello".to_owned()); - /// let x_ptr = Rc::into_raw(x); - /// assert_eq!(unsafe { &*x_ptr }, "hello"); - /// ``` - #[stable(feature = "rc_raw", since = "1.17.0")] - pub fn into_raw(this: Self) -> *const T { - let ptr = Self::as_ptr(&this); - mem::forget(this); - ptr - } - - /// Provides a raw pointer to the data. - /// - /// The counts are not affected in any way and the `Rc` is not consumed. The pointer is valid - /// for as long there are strong counts in the `Rc`. - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let x = Rc::new("hello".to_owned()); - /// let y = Rc::clone(&x); - /// let x_ptr = Rc::as_ptr(&x); - /// assert_eq!(x_ptr, Rc::as_ptr(&y)); - /// assert_eq!(unsafe { &*x_ptr }, "hello"); - /// ``` - #[stable(feature = "weak_into_raw", since = "1.45.0")] - pub fn as_ptr(this: &Self) -> *const T { - let ptr: *mut RcBox<T> = NonNull::as_ptr(this.ptr); - - // SAFETY: This cannot go through Deref::deref or Rc::inner because - // this is required to retain raw/mut provenance such that e.g. `get_mut` can - // write through the pointer after the Rc is recovered through `from_raw`. - unsafe { &raw const (*ptr).value } - } - - /// Constructs an `Rc<T>` from a raw pointer. - /// - /// The raw pointer must have been previously returned by a call to - /// [`Rc<U>::into_raw`][into_raw] where `U` must have the same size - /// and alignment as `T`. This is trivially true if `U` is `T`. - /// Note that if `U` is not `T` but has the same size and alignment, this is - /// basically like transmuting references of different types. See - /// [`mem::transmute`][transmute] for more information on what - /// restrictions apply in this case. - /// - /// The user of `from_raw` has to make sure a specific value of `T` is only - /// dropped once. - /// - /// This function is unsafe because improper use may lead to memory unsafety, - /// even if the returned `Rc<T>` is never accessed. - /// - /// [into_raw]: struct.Rc.html#method.into_raw - /// [transmute]: ../../std/mem/fn.transmute.html - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let x = Rc::new("hello".to_owned()); - /// let x_ptr = Rc::into_raw(x); - /// - /// unsafe { - /// // Convert back to an `Rc` to prevent leak. - /// let x = Rc::from_raw(x_ptr); - /// assert_eq!(&*x, "hello"); - /// - /// // Further calls to `Rc::from_raw(x_ptr)` would be memory-unsafe. - /// } - /// - /// // The memory was freed when `x` went out of scope above, so `x_ptr` is now dangling! - /// ``` - #[stable(feature = "rc_raw", since = "1.17.0")] - pub unsafe fn from_raw(ptr: *const T) -> Self { - let offset = unsafe { data_offset(ptr) }; - - // Reverse the offset to find the original RcBox. - let fake_ptr = ptr as *mut RcBox<T>; - let rc_ptr = unsafe { set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset)) }; - - unsafe { Self::from_ptr(rc_ptr) } - } - - /// Consumes the `Rc`, returning the wrapped pointer as `NonNull<T>`. - /// - /// # Examples - /// - /// ``` - /// #![feature(rc_into_raw_non_null)] - /// #![allow(deprecated)] - /// - /// use std::rc::Rc; - /// - /// let x = Rc::new("hello".to_owned()); - /// let ptr = Rc::into_raw_non_null(x); - /// let deref = unsafe { ptr.as_ref() }; - /// assert_eq!(deref, "hello"); - /// ``` - #[unstable(feature = "rc_into_raw_non_null", issue = "47336")] - #[rustc_deprecated(since = "1.44.0", reason = "use `Rc::into_raw` instead")] - #[inline] - pub fn into_raw_non_null(this: Self) -> NonNull<T> { - // safe because Rc guarantees its pointer is non-null - unsafe { NonNull::new_unchecked(Rc::into_raw(this) as *mut _) } - } - - /// Creates a new [`Weak`][weak] pointer to this allocation. - /// - /// [weak]: struct.Weak.html - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let five = Rc::new(5); - /// - /// let weak_five = Rc::downgrade(&five); - /// ``` - #[stable(feature = "rc_weak", since = "1.4.0")] - pub fn downgrade(this: &Self) -> Weak<T> { - this.inc_weak(); - // Make sure we do not create a dangling Weak - debug_assert!(!is_dangling(this.ptr)); - Weak { ptr: this.ptr } - } - - /// Gets the number of [`Weak`][weak] pointers to this allocation. - /// - /// [weak]: struct.Weak.html - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let five = Rc::new(5); - /// let _weak_five = Rc::downgrade(&five); - /// - /// assert_eq!(1, Rc::weak_count(&five)); - /// ``` - #[inline] - #[stable(feature = "rc_counts", since = "1.15.0")] - pub fn weak_count(this: &Self) -> usize { - this.weak() - 1 - } - - /// Gets the number of strong (`Rc`) pointers to this allocation. - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let five = Rc::new(5); - /// let _also_five = Rc::clone(&five); - /// - /// assert_eq!(2, Rc::strong_count(&five)); - /// ``` - #[inline] - #[stable(feature = "rc_counts", since = "1.15.0")] - pub fn strong_count(this: &Self) -> usize { - this.strong() - } - - /// Returns `true` if there are no other `Rc` or [`Weak`][weak] pointers to - /// this allocation. - /// - /// [weak]: struct.Weak.html - #[inline] - fn is_unique(this: &Self) -> bool { - Rc::weak_count(this) == 0 && Rc::strong_count(this) == 1 - } - - /// Returns a mutable reference into the given `Rc`, if there are - /// no other `Rc` or [`Weak`][weak] pointers to the same allocation. - /// - /// Returns [`None`] otherwise, because it is not safe to - /// mutate a shared value. - /// - /// See also [`make_mut`][make_mut], which will [`clone`][clone] - /// the inner value when there are other pointers. - /// - /// [weak]: struct.Weak.html - /// [`None`]: ../../std/option/enum.Option.html#variant.None - /// [make_mut]: struct.Rc.html#method.make_mut - /// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let mut x = Rc::new(3); - /// *Rc::get_mut(&mut x).unwrap() = 4; - /// assert_eq!(*x, 4); - /// - /// let _y = Rc::clone(&x); - /// assert!(Rc::get_mut(&mut x).is_none()); - /// ``` - #[inline] - #[stable(feature = "rc_unique", since = "1.4.0")] - pub fn get_mut(this: &mut Self) -> Option<&mut T> { - if Rc::is_unique(this) { unsafe { Some(Rc::get_mut_unchecked(this)) } } else { None } - } - - /// Returns a mutable reference into the given `Rc`, - /// without any check. - /// - /// See also [`get_mut`], which is safe and does appropriate checks. - /// - /// [`get_mut`]: struct.Rc.html#method.get_mut - /// - /// # Safety - /// - /// Any other `Rc` or [`Weak`] pointers to the same allocation must not be dereferenced - /// for the duration of the returned borrow. - /// This is trivially the case if no such pointers exist, - /// for example immediately after `Rc::new`. - /// - /// # Examples - /// - /// ``` - /// #![feature(get_mut_unchecked)] - /// - /// use std::rc::Rc; - /// - /// let mut x = Rc::new(String::new()); - /// unsafe { - /// Rc::get_mut_unchecked(&mut x).push_str("foo") - /// } - /// assert_eq!(*x, "foo"); - /// ``` - #[inline] - #[unstable(feature = "get_mut_unchecked", issue = "63292")] - pub unsafe fn get_mut_unchecked(this: &mut Self) -> &mut T { - unsafe { &mut this.ptr.as_mut().value } - } - - #[inline] - #[stable(feature = "ptr_eq", since = "1.17.0")] - /// Returns `true` if the two `Rc`s point to the same allocation - /// (in a vein similar to [`ptr::eq`]). - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let five = Rc::new(5); - /// let same_five = Rc::clone(&five); - /// let other_five = Rc::new(5); - /// - /// assert!(Rc::ptr_eq(&five, &same_five)); - /// assert!(!Rc::ptr_eq(&five, &other_five)); - /// ``` - /// - /// [`ptr::eq`]: ../../std/ptr/fn.eq.html - pub fn ptr_eq(this: &Self, other: &Self) -> bool { - this.ptr.as_ptr() == other.ptr.as_ptr() - } -} - -impl<T: Clone> Rc<T> { - /// Makes a mutable reference into the given `Rc`. - /// - /// If there are other `Rc` pointers to the same allocation, then `make_mut` will - /// [`clone`] the inner value to a new allocation to ensure unique ownership. This is also - /// referred to as clone-on-write. - /// - /// If there are no other `Rc` pointers to this allocation, then [`Weak`] - /// pointers to this allocation will be disassociated. - /// - /// See also [`get_mut`], which will fail rather than cloning. - /// - /// [`Weak`]: struct.Weak.html - /// [`clone`]: ../../std/clone/trait.Clone.html#tymethod.clone - /// [`get_mut`]: struct.Rc.html#method.get_mut - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let mut data = Rc::new(5); - /// - /// *Rc::make_mut(&mut data) += 1; // Won't clone anything - /// let mut other_data = Rc::clone(&data); // Won't clone inner data - /// *Rc::make_mut(&mut data) += 1; // Clones inner data - /// *Rc::make_mut(&mut data) += 1; // Won't clone anything - /// *Rc::make_mut(&mut other_data) *= 2; // Won't clone anything - /// - /// // Now `data` and `other_data` point to different allocations. - /// assert_eq!(*data, 8); - /// assert_eq!(*other_data, 12); - /// ``` - /// - /// [`Weak`] pointers will be disassociated: - /// - /// ``` - /// use std::rc::Rc; - /// - /// let mut data = Rc::new(75); - /// let weak = Rc::downgrade(&data); - /// - /// assert!(75 == *data); - /// assert!(75 == *weak.upgrade().unwrap()); - /// - /// *Rc::make_mut(&mut data) += 1; - /// - /// assert!(76 == *data); - /// assert!(weak.upgrade().is_none()); - /// ``` - #[inline] - #[stable(feature = "rc_unique", since = "1.4.0")] - pub fn make_mut(this: &mut Self) -> &mut T { - if Rc::strong_count(this) != 1 { - // Gotta clone the data, there are other Rcs - *this = Rc::new((**this).clone()) - } else if Rc::weak_count(this) != 0 { - // Can just steal the data, all that's left is Weaks - unsafe { - let mut swap = Rc::new(ptr::read(&this.ptr.as_ref().value)); - mem::swap(this, &mut swap); - swap.dec_strong(); - // Remove implicit strong-weak ref (no need to craft a fake - // Weak here -- we know other Weaks can clean up for us) - swap.dec_weak(); - forget(swap); - } - } - // This unsafety is ok because we're guaranteed that the pointer - // returned is the *only* pointer that will ever be returned to T. Our - // reference count is guaranteed to be 1 at this point, and we required - // the `Rc<T>` itself to be `mut`, so we're returning the only possible - // reference to the allocation. - unsafe { &mut this.ptr.as_mut().value } - } -} - -impl Rc<dyn Any> { - #[inline] - #[stable(feature = "rc_downcast", since = "1.29.0")] - /// Attempt to downcast the `Rc<dyn Any>` to a concrete type. - /// - /// # Examples - /// - /// ``` - /// use std::any::Any; - /// use std::rc::Rc; - /// - /// fn print_if_string(value: Rc<dyn Any>) { - /// if let Ok(string) = value.downcast::<String>() { - /// println!("String ({}): {}", string.len(), string); - /// } - /// } - /// - /// let my_string = "Hello World".to_string(); - /// print_if_string(Rc::new(my_string)); - /// print_if_string(Rc::new(0i8)); - /// ``` - pub fn downcast<T: Any>(self) -> Result<Rc<T>, Rc<dyn Any>> { - if (*self).is::<T>() { - let ptr = self.ptr.cast::<RcBox<T>>(); - forget(self); - Ok(Rc::from_inner(ptr)) - } else { - Err(self) - } - } -} - -impl<T: ?Sized> Rc<T> { - /// Allocates an `RcBox<T>` with sufficient space for - /// a possibly-unsized inner value where the value has the layout provided. - /// - /// The function `mem_to_rcbox` is called with the data pointer - /// and must return back a (potentially fat)-pointer for the `RcBox<T>`. - unsafe fn allocate_for_layout( - value_layout: Layout, - mem_to_rcbox: impl FnOnce(*mut u8) -> *mut RcBox<T>, - ) -> *mut RcBox<T> { - // Calculate layout using the given value layout. - // Previously, layout was calculated on the expression - // `&*(ptr as *const RcBox<T>)`, but this created a misaligned - // reference (see #54908). - let layout = Layout::new::<RcBox<()>>().extend(value_layout).unwrap().0.pad_to_align(); - - // Allocate for the layout. - let mem = Global - .alloc(layout, AllocInit::Uninitialized) - .unwrap_or_else(|_| handle_alloc_error(layout)); - - // Initialize the RcBox - let inner = mem_to_rcbox(mem.ptr.as_ptr()); - unsafe { - debug_assert_eq!(Layout::for_value(&*inner), layout); - - ptr::write(&mut (*inner).strong, Cell::new(1)); - ptr::write(&mut (*inner).weak, Cell::new(1)); - } - - inner - } - - /// Allocates an `RcBox<T>` with sufficient space for an unsized inner value - unsafe fn allocate_for_ptr(ptr: *const T) -> *mut RcBox<T> { - // Allocate for the `RcBox<T>` using the given value. - unsafe { - Self::allocate_for_layout(Layout::for_value(&*ptr), |mem| { - set_data_ptr(ptr as *mut T, mem) as *mut RcBox<T> - }) - } - } - - fn from_box(v: Box<T>) -> Rc<T> { - unsafe { - let box_unique = Box::into_unique(v); - let bptr = box_unique.as_ptr(); - - let value_size = size_of_val(&*bptr); - let ptr = Self::allocate_for_ptr(bptr); - - // Copy value as bytes - ptr::copy_nonoverlapping( - bptr as *const T as *const u8, - &mut (*ptr).value as *mut _ as *mut u8, - value_size, - ); - - // Free the allocation without dropping its contents - box_free(box_unique); - - Self::from_ptr(ptr) - } - } -} - -impl<T> Rc<[T]> { - /// Allocates an `RcBox<[T]>` with the given length. - unsafe fn allocate_for_slice(len: usize) -> *mut RcBox<[T]> { - unsafe { - Self::allocate_for_layout(Layout::array::<T>(len).unwrap(), |mem| { - ptr::slice_from_raw_parts_mut(mem as *mut T, len) as *mut RcBox<[T]> - }) - } - } -} - -/// Sets the data pointer of a `?Sized` raw pointer. -/// -/// For a slice/trait object, this sets the `data` field and leaves the rest -/// unchanged. For a sized raw pointer, this simply sets the pointer. -unsafe fn set_data_ptr<T: ?Sized, U>(mut ptr: *mut T, data: *mut U) -> *mut T { - unsafe { - ptr::write(&mut ptr as *mut _ as *mut *mut u8, data as *mut u8); - } - ptr -} - -impl<T> Rc<[T]> { - /// Copy elements from slice into newly allocated Rc<\[T\]> - /// - /// Unsafe because the caller must either take ownership or bind `T: Copy` - unsafe fn copy_from_slice(v: &[T]) -> Rc<[T]> { - unsafe { - let ptr = Self::allocate_for_slice(v.len()); - ptr::copy_nonoverlapping(v.as_ptr(), &mut (*ptr).value as *mut [T] as *mut T, v.len()); - Self::from_ptr(ptr) - } - } - - /// Constructs an `Rc<[T]>` from an iterator known to be of a certain size. - /// - /// Behavior is undefined should the size be wrong. - unsafe fn from_iter_exact(iter: impl iter::Iterator<Item = T>, len: usize) -> Rc<[T]> { - // Panic guard while cloning T elements. - // In the event of a panic, elements that have been written - // into the new RcBox will be dropped, then the memory freed. - struct Guard<T> { - mem: NonNull<u8>, - elems: *mut T, - layout: Layout, - n_elems: usize, - } - - impl<T> Drop for Guard<T> { - fn drop(&mut self) { - unsafe { - let slice = from_raw_parts_mut(self.elems, self.n_elems); - ptr::drop_in_place(slice); - - Global.dealloc(self.mem, self.layout); - } - } - } - - unsafe { - let ptr = Self::allocate_for_slice(len); - - let mem = ptr as *mut _ as *mut u8; - let layout = Layout::for_value(&*ptr); - - // Pointer to first element - let elems = &mut (*ptr).value as *mut [T] as *mut T; - - let mut guard = Guard { mem: NonNull::new_unchecked(mem), elems, layout, n_elems: 0 }; - - for (i, item) in iter.enumerate() { - ptr::write(elems.add(i), item); - guard.n_elems += 1; - } - - // All clear. Forget the guard so it doesn't free the new RcBox. - forget(guard); - - Self::from_ptr(ptr) - } - } -} - -/// Specialization trait used for `From<&[T]>`. -trait RcFromSlice<T> { - fn from_slice(slice: &[T]) -> Self; -} - -impl<T: Clone> RcFromSlice<T> for Rc<[T]> { - #[inline] - default fn from_slice(v: &[T]) -> Self { - unsafe { Self::from_iter_exact(v.iter().cloned(), v.len()) } - } -} - -impl<T: Copy> RcFromSlice<T> for Rc<[T]> { - #[inline] - fn from_slice(v: &[T]) -> Self { - unsafe { Rc::copy_from_slice(v) } - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl<T: ?Sized> Deref for Rc<T> { - type Target = T; - - #[inline(always)] - fn deref(&self) -> &T { - &self.inner().value - } -} - -#[unstable(feature = "receiver_trait", issue = "none")] -impl<T: ?Sized> Receiver for Rc<T> {} - -#[stable(feature = "rust1", since = "1.0.0")] -unsafe impl<#[may_dangle] T: ?Sized> Drop for Rc<T> { - /// Drops the `Rc`. - /// - /// This will decrement the strong reference count. If the strong reference - /// count reaches zero then the only other references (if any) are - /// [`Weak`], so we `drop` the inner value. - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// struct Foo; - /// - /// impl Drop for Foo { - /// fn drop(&mut self) { - /// println!("dropped!"); - /// } - /// } - /// - /// let foo = Rc::new(Foo); - /// let foo2 = Rc::clone(&foo); - /// - /// drop(foo); // Doesn't print anything - /// drop(foo2); // Prints "dropped!" - /// ``` - /// - /// [`Weak`]: ../../std/rc/struct.Weak.html - fn drop(&mut self) { - unsafe { - self.dec_strong(); - if self.strong() == 0 { - // destroy the contained object - ptr::drop_in_place(self.ptr.as_mut()); - - // remove the implicit "strong weak" pointer now that we've - // destroyed the contents. - self.dec_weak(); - - if self.weak() == 0 { - Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref())); - } - } - } - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl<T: ?Sized> Clone for Rc<T> { - /// Makes a clone of the `Rc` pointer. - /// - /// This creates another pointer to the same allocation, increasing the - /// strong reference count. - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let five = Rc::new(5); - /// - /// let _ = Rc::clone(&five); - /// ``` - #[inline] - fn clone(&self) -> Rc<T> { - self.inc_strong(); - Self::from_inner(self.ptr) - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl<T: Default> Default for Rc<T> { - /// Creates a new `Rc<T>`, with the `Default` value for `T`. - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let x: Rc<i32> = Default::default(); - /// assert_eq!(*x, 0); - /// ``` - #[inline] - fn default() -> Rc<T> { - Rc::new(Default::default()) - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -trait RcEqIdent<T: ?Sized + PartialEq> { - fn eq(&self, other: &Rc<T>) -> bool; - fn ne(&self, other: &Rc<T>) -> bool; -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl<T: ?Sized + PartialEq> RcEqIdent<T> for Rc<T> { - #[inline] - default fn eq(&self, other: &Rc<T>) -> bool { - **self == **other - } - - #[inline] - default fn ne(&self, other: &Rc<T>) -> bool { - **self != **other - } -} - -// Hack to allow specializing on `Eq` even though `Eq` has a method. -#[rustc_unsafe_specialization_marker] -pub(crate) trait MarkerEq: PartialEq<Self> {} - -impl<T: Eq> MarkerEq for T {} - -/// We're doing this specialization here, and not as a more general optimization on `&T`, because it -/// would otherwise add a cost to all equality checks on refs. We assume that `Rc`s are used to -/// store large values, that are slow to clone, but also heavy to check for equality, causing this -/// cost to pay off more easily. It's also more likely to have two `Rc` clones, that point to -/// the same value, than two `&T`s. -/// -/// We can only do this when `T: Eq` as a `PartialEq` might be deliberately irreflexive. -#[stable(feature = "rust1", since = "1.0.0")] -impl<T: ?Sized + MarkerEq> RcEqIdent<T> for Rc<T> { - #[inline] - fn eq(&self, other: &Rc<T>) -> bool { - Rc::ptr_eq(self, other) || **self == **other - } - - #[inline] - fn ne(&self, other: &Rc<T>) -> bool { - !Rc::ptr_eq(self, other) && **self != **other - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl<T: ?Sized + PartialEq> PartialEq for Rc<T> { - /// Equality for two `Rc`s. - /// - /// Two `Rc`s are equal if their inner values are equal, even if they are - /// stored in different allocation. - /// - /// If `T` also implements `Eq` (implying reflexivity of equality), - /// two `Rc`s that point to the same allocation are - /// always equal. - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let five = Rc::new(5); - /// - /// assert!(five == Rc::new(5)); - /// ``` - #[inline] - fn eq(&self, other: &Rc<T>) -> bool { - RcEqIdent::eq(self, other) - } - - /// Inequality for two `Rc`s. - /// - /// Two `Rc`s are unequal if their inner values are unequal. - /// - /// If `T` also implements `Eq` (implying reflexivity of equality), - /// two `Rc`s that point to the same allocation are - /// never unequal. - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let five = Rc::new(5); - /// - /// assert!(five != Rc::new(6)); - /// ``` - #[inline] - fn ne(&self, other: &Rc<T>) -> bool { - RcEqIdent::ne(self, other) - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl<T: ?Sized + Eq> Eq for Rc<T> {} - -#[stable(feature = "rust1", since = "1.0.0")] -impl<T: ?Sized + PartialOrd> PartialOrd for Rc<T> { - /// Partial comparison for two `Rc`s. - /// - /// The two are compared by calling `partial_cmp()` on their inner values. - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// use std::cmp::Ordering; - /// - /// let five = Rc::new(5); - /// - /// assert_eq!(Some(Ordering::Less), five.partial_cmp(&Rc::new(6))); - /// ``` - #[inline(always)] - fn partial_cmp(&self, other: &Rc<T>) -> Option<Ordering> { - (**self).partial_cmp(&**other) - } - - /// Less-than comparison for two `Rc`s. - /// - /// The two are compared by calling `<` on their inner values. - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let five = Rc::new(5); - /// - /// assert!(five < Rc::new(6)); - /// ``` - #[inline(always)] - fn lt(&self, other: &Rc<T>) -> bool { - **self < **other - } - - /// 'Less than or equal to' comparison for two `Rc`s. - /// - /// The two are compared by calling `<=` on their inner values. - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let five = Rc::new(5); - /// - /// assert!(five <= Rc::new(5)); - /// ``` - #[inline(always)] - fn le(&self, other: &Rc<T>) -> bool { - **self <= **other - } - - /// Greater-than comparison for two `Rc`s. - /// - /// The two are compared by calling `>` on their inner values. - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let five = Rc::new(5); - /// - /// assert!(five > Rc::new(4)); - /// ``` - #[inline(always)] - fn gt(&self, other: &Rc<T>) -> bool { - **self > **other - } - - /// 'Greater than or equal to' comparison for two `Rc`s. - /// - /// The two are compared by calling `>=` on their inner values. - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let five = Rc::new(5); - /// - /// assert!(five >= Rc::new(5)); - /// ``` - #[inline(always)] - fn ge(&self, other: &Rc<T>) -> bool { - **self >= **other - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl<T: ?Sized + Ord> Ord for Rc<T> { - /// Comparison for two `Rc`s. - /// - /// The two are compared by calling `cmp()` on their inner values. - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// use std::cmp::Ordering; - /// - /// let five = Rc::new(5); - /// - /// assert_eq!(Ordering::Less, five.cmp(&Rc::new(6))); - /// ``` - #[inline] - fn cmp(&self, other: &Rc<T>) -> Ordering { - (**self).cmp(&**other) - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl<T: ?Sized + Hash> Hash for Rc<T> { - fn hash<H: Hasher>(&self, state: &mut H) { - (**self).hash(state); - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl<T: ?Sized + fmt::Display> fmt::Display for Rc<T> { - fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - fmt::Display::fmt(&**self, f) - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl<T: ?Sized + fmt::Debug> fmt::Debug for Rc<T> { - fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - fmt::Debug::fmt(&**self, f) - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl<T: ?Sized> fmt::Pointer for Rc<T> { - fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - fmt::Pointer::fmt(&(&**self as *const T), f) - } -} - -#[stable(feature = "from_for_ptrs", since = "1.6.0")] -impl<T> From<T> for Rc<T> { - fn from(t: T) -> Self { - Rc::new(t) - } -} - -#[stable(feature = "shared_from_slice", since = "1.21.0")] -impl<T: Clone> From<&[T]> for Rc<[T]> { - #[inline] - fn from(v: &[T]) -> Rc<[T]> { - <Self as RcFromSlice<T>>::from_slice(v) - } -} - -#[stable(feature = "shared_from_slice", since = "1.21.0")] -impl From<&str> for Rc<str> { - #[inline] - fn from(v: &str) -> Rc<str> { - let rc = Rc::<[u8]>::from(v.as_bytes()); - unsafe { Rc::from_raw(Rc::into_raw(rc) as *const str) } - } -} - -#[stable(feature = "shared_from_slice", since = "1.21.0")] -impl From<String> for Rc<str> { - #[inline] - fn from(v: String) -> Rc<str> { - Rc::from(&v[..]) - } -} - -#[stable(feature = "shared_from_slice", since = "1.21.0")] -impl<T: ?Sized> From<Box<T>> for Rc<T> { - #[inline] - fn from(v: Box<T>) -> Rc<T> { - Rc::from_box(v) - } -} - -#[stable(feature = "shared_from_slice", since = "1.21.0")] -impl<T> From<Vec<T>> for Rc<[T]> { - #[inline] - fn from(mut v: Vec<T>) -> Rc<[T]> { - unsafe { - let rc = Rc::copy_from_slice(&v); - - // Allow the Vec to free its memory, but not destroy its contents - v.set_len(0); - - rc - } - } -} - -#[stable(feature = "shared_from_cow", since = "1.45.0")] -impl<'a, B> From<Cow<'a, B>> for Rc<B> -where - B: ToOwned + ?Sized, - Rc<B>: From<&'a B> + From<B::Owned>, -{ - #[inline] - fn from(cow: Cow<'a, B>) -> Rc<B> { - match cow { - Cow::Borrowed(s) => Rc::from(s), - Cow::Owned(s) => Rc::from(s), - } - } -} - -#[stable(feature = "boxed_slice_try_from", since = "1.43.0")] -impl<T, const N: usize> TryFrom<Rc<[T]>> for Rc<[T; N]> { - type Error = Rc<[T]>; - - fn try_from(boxed_slice: Rc<[T]>) -> Result<Self, Self::Error> { - if boxed_slice.len() == N { - Ok(unsafe { Rc::from_raw(Rc::into_raw(boxed_slice) as *mut [T; N]) }) - } else { - Err(boxed_slice) - } - } -} - -#[stable(feature = "shared_from_iter", since = "1.37.0")] -impl<T> iter::FromIterator<T> for Rc<[T]> { - /// Takes each element in the `Iterator` and collects it into an `Rc<[T]>`. - /// - /// # Performance characteristics - /// - /// ## The general case - /// - /// In the general case, collecting into `Rc<[T]>` is done by first - /// collecting into a `Vec<T>`. That is, when writing the following: - /// - /// ```rust - /// # use std::rc::Rc; - /// let evens: Rc<[u8]> = (0..10).filter(|&x| x % 2 == 0).collect(); - /// # assert_eq!(&*evens, &[0, 2, 4, 6, 8]); - /// ``` - /// - /// this behaves as if we wrote: - /// - /// ```rust - /// # use std::rc::Rc; - /// let evens: Rc<[u8]> = (0..10).filter(|&x| x % 2 == 0) - /// .collect::<Vec<_>>() // The first set of allocations happens here. - /// .into(); // A second allocation for `Rc<[T]>` happens here. - /// # assert_eq!(&*evens, &[0, 2, 4, 6, 8]); - /// ``` - /// - /// This will allocate as many times as needed for constructing the `Vec<T>` - /// and then it will allocate once for turning the `Vec<T>` into the `Rc<[T]>`. - /// - /// ## Iterators of known length - /// - /// When your `Iterator` implements `TrustedLen` and is of an exact size, - /// a single allocation will be made for the `Rc<[T]>`. For example: - /// - /// ```rust - /// # use std::rc::Rc; - /// let evens: Rc<[u8]> = (0..10).collect(); // Just a single allocation happens here. - /// # assert_eq!(&*evens, &*(0..10).collect::<Vec<_>>()); - /// ``` - fn from_iter<I: iter::IntoIterator<Item = T>>(iter: I) -> Self { - ToRcSlice::to_rc_slice(iter.into_iter()) - } -} - -/// Specialization trait used for collecting into `Rc<[T]>`. -trait ToRcSlice<T>: Iterator<Item = T> + Sized { - fn to_rc_slice(self) -> Rc<[T]>; -} - -impl<T, I: Iterator<Item = T>> ToRcSlice<T> for I { - default fn to_rc_slice(self) -> Rc<[T]> { - self.collect::<Vec<T>>().into() - } -} - -impl<T, I: iter::TrustedLen<Item = T>> ToRcSlice<T> for I { - fn to_rc_slice(self) -> Rc<[T]> { - // This is the case for a `TrustedLen` iterator. - let (low, high) = self.size_hint(); - if let Some(high) = high { - debug_assert_eq!( - low, - high, - "TrustedLen iterator's size hint is not exact: {:?}", - (low, high) - ); - - unsafe { - // SAFETY: We need to ensure that the iterator has an exact length and we have. - Rc::from_iter_exact(self, low) - } - } else { - // Fall back to normal implementation. - self.collect::<Vec<T>>().into() - } - } -} - -/// `Weak` is a version of [`Rc`] that holds a non-owning reference to the -/// managed allocation. The allocation is accessed by calling [`upgrade`] on the `Weak` -/// pointer, which returns an [`Option`]`<`[`Rc`]`<T>>`. -/// -/// Since a `Weak` reference does not count towards ownership, it will not -/// prevent the value stored in the allocation from being dropped, and `Weak` itself makes no -/// guarantees about the value still being present. Thus it may return [`None`] -/// when [`upgrade`]d. Note however that a `Weak` reference *does* prevent the allocation -/// itself (the backing store) from being deallocated. -/// -/// A `Weak` pointer is useful for keeping a temporary reference to the allocation -/// managed by [`Rc`] without preventing its inner value from being dropped. It is also used to -/// prevent circular references between [`Rc`] pointers, since mutual owning references -/// would never allow either [`Rc`] to be dropped. For example, a tree could -/// have strong [`Rc`] pointers from parent nodes to children, and `Weak` -/// pointers from children back to their parents. -/// -/// The typical way to obtain a `Weak` pointer is to call [`Rc::downgrade`]. -/// -/// [`Rc`]: struct.Rc.html -/// [`Rc::downgrade`]: struct.Rc.html#method.downgrade -/// [`upgrade`]: struct.Weak.html#method.upgrade -/// [`Option`]: ../../std/option/enum.Option.html -/// [`None`]: ../../std/option/enum.Option.html#variant.None -#[stable(feature = "rc_weak", since = "1.4.0")] -pub struct Weak<T: ?Sized> { - // This is a `NonNull` to allow optimizing the size of this type in enums, - // but it is not necessarily a valid pointer. - // `Weak::new` sets this to `usize::MAX` so that it doesn’t need - // to allocate space on the heap. That's not a value a real pointer - // will ever have because RcBox has alignment at least 2. - // This is only possible when `T: Sized`; unsized `T` never dangle. - ptr: NonNull<RcBox<T>>, -} - -#[stable(feature = "rc_weak", since = "1.4.0")] -impl<T: ?Sized> !marker::Send for Weak<T> {} -#[stable(feature = "rc_weak", since = "1.4.0")] -impl<T: ?Sized> !marker::Sync for Weak<T> {} - -#[unstable(feature = "coerce_unsized", issue = "27732")] -impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {} - -#[unstable(feature = "dispatch_from_dyn", issue = "none")] -impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Weak<U>> for Weak<T> {} - -impl<T> Weak<T> { - /// Constructs a new `Weak<T>`, without allocating any memory. - /// Calling [`upgrade`] on the return value always gives [`None`]. - /// - /// [`upgrade`]: #method.upgrade - /// [`None`]: ../../std/option/enum.Option.html - /// - /// # Examples - /// - /// ``` - /// use std::rc::Weak; - /// - /// let empty: Weak<i64> = Weak::new(); - /// assert!(empty.upgrade().is_none()); - /// ``` - #[stable(feature = "downgraded_weak", since = "1.10.0")] - pub fn new() -> Weak<T> { - Weak { ptr: NonNull::new(usize::MAX as *mut RcBox<T>).expect("MAX is not 0") } - } - - /// Returns a raw pointer to the object `T` pointed to by this `Weak<T>`. - /// - /// The pointer is valid only if there are some strong references. The pointer may be dangling, - /// unaligned or even [`null`] otherwise. - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// use std::ptr; - /// - /// let strong = Rc::new("hello".to_owned()); - /// let weak = Rc::downgrade(&strong); - /// // Both point to the same object - /// assert!(ptr::eq(&*strong, weak.as_ptr())); - /// // The strong here keeps it alive, so we can still access the object. - /// assert_eq!("hello", unsafe { &*weak.as_ptr() }); - /// - /// drop(strong); - /// // But not any more. We can do weak.as_ptr(), but accessing the pointer would lead to - /// // undefined behaviour. - /// // assert_eq!("hello", unsafe { &*weak.as_ptr() }); - /// ``` - /// - /// [`null`]: ../../std/ptr/fn.null.html - #[stable(feature = "rc_as_ptr", since = "1.45.0")] - pub fn as_ptr(&self) -> *const T { - let ptr: *mut RcBox<T> = NonNull::as_ptr(self.ptr); - - // SAFETY: we must offset the pointer manually, and said pointer may be - // a dangling weak (usize::MAX) if T is sized. data_offset is safe to call, - // because we know that a pointer to unsized T was derived from a real - // unsized T, as dangling weaks are only created for sized T. wrapping_offset - // is used so that we can use the same code path for the non-dangling - // unsized case and the potentially dangling sized case. - unsafe { - let offset = data_offset(ptr as *mut T); - set_data_ptr(ptr as *mut T, (ptr as *mut u8).wrapping_offset(offset)) - } - } - - /// Consumes the `Weak<T>` and turns it into a raw pointer. - /// - /// This converts the weak pointer into a raw pointer, preserving the original weak count. It - /// can be turned back into the `Weak<T>` with [`from_raw`]. - /// - /// The same restrictions of accessing the target of the pointer as with - /// [`as_ptr`] apply. - /// - /// # Examples - /// - /// ``` - /// use std::rc::{Rc, Weak}; - /// - /// let strong = Rc::new("hello".to_owned()); - /// let weak = Rc::downgrade(&strong); - /// let raw = weak.into_raw(); - /// - /// assert_eq!(1, Rc::weak_count(&strong)); - /// assert_eq!("hello", unsafe { &*raw }); - /// - /// drop(unsafe { Weak::from_raw(raw) }); - /// assert_eq!(0, Rc::weak_count(&strong)); - /// ``` - /// - /// [`from_raw`]: struct.Weak.html#method.from_raw - /// [`as_ptr`]: struct.Weak.html#method.as_ptr - #[stable(feature = "weak_into_raw", since = "1.45.0")] - pub fn into_raw(self) -> *const T { - let result = self.as_ptr(); - mem::forget(self); - result - } - - /// Converts a raw pointer previously created by [`into_raw`] back into `Weak<T>`. - /// - /// This can be used to safely get a strong reference (by calling [`upgrade`] - /// later) or to deallocate the weak count by dropping the `Weak<T>`. - /// - /// It takes ownership of one weak count (with the exception of pointers created by [`new`], - /// as these don't have any corresponding weak count). - /// - /// # Safety - /// - /// The pointer must have originated from the [`into_raw`] and must still own its potential - /// weak reference count. - /// - /// It is allowed for the strong count to be 0 at the time of calling this, but the weak count - /// must be non-zero or the pointer must have originated from a dangling `Weak<T>` (one created - /// by [`new`]). - /// - /// # Examples - /// - /// ``` - /// use std::rc::{Rc, Weak}; - /// - /// let strong = Rc::new("hello".to_owned()); - /// - /// let raw_1 = Rc::downgrade(&strong).into_raw(); - /// let raw_2 = Rc::downgrade(&strong).into_raw(); - /// - /// assert_eq!(2, Rc::weak_count(&strong)); - /// - /// assert_eq!("hello", &*unsafe { Weak::from_raw(raw_1) }.upgrade().unwrap()); - /// assert_eq!(1, Rc::weak_count(&strong)); - /// - /// drop(strong); - /// - /// // Decrement the last weak count. - /// assert!(unsafe { Weak::from_raw(raw_2) }.upgrade().is_none()); - /// ``` - /// - /// [`into_raw`]: struct.Weak.html#method.into_raw - /// [`upgrade`]: struct.Weak.html#method.upgrade - /// [`Rc`]: struct.Rc.html - /// [`Weak`]: struct.Weak.html - /// [`new`]: struct.Weak.html#method.new - /// [`forget`]: ../../std/mem/fn.forget.html - #[stable(feature = "weak_into_raw", since = "1.45.0")] - pub unsafe fn from_raw(ptr: *const T) -> Self { - if ptr.is_null() { - Self::new() - } else { - // See Rc::from_raw for details - unsafe { - let offset = data_offset(ptr); - let fake_ptr = ptr as *mut RcBox<T>; - let ptr = set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset)); - Weak { ptr: NonNull::new(ptr).expect("Invalid pointer passed to from_raw") } - } - } - } -} - -pub(crate) fn is_dangling<T: ?Sized>(ptr: NonNull<T>) -> bool { - let address = ptr.as_ptr() as *mut () as usize; - address == usize::MAX -} - -impl<T: ?Sized> Weak<T> { - /// Attempts to upgrade the `Weak` pointer to an [`Rc`], delaying - /// dropping of the inner value if successful. - /// - /// Returns [`None`] if the inner value has since been dropped. - /// - /// [`Rc`]: struct.Rc.html - /// [`None`]: ../../std/option/enum.Option.html - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let five = Rc::new(5); - /// - /// let weak_five = Rc::downgrade(&five); - /// - /// let strong_five: Option<Rc<_>> = weak_five.upgrade(); - /// assert!(strong_five.is_some()); - /// - /// // Destroy all strong pointers. - /// drop(strong_five); - /// drop(five); - /// - /// assert!(weak_five.upgrade().is_none()); - /// ``` - #[stable(feature = "rc_weak", since = "1.4.0")] - pub fn upgrade(&self) -> Option<Rc<T>> { - let inner = self.inner()?; - if inner.strong() == 0 { - None - } else { - inner.inc_strong(); - Some(Rc::from_inner(self.ptr)) - } - } - - /// Gets the number of strong (`Rc`) pointers pointing to this allocation. - /// - /// If `self` was created using [`Weak::new`], this will return 0. - /// - /// [`Weak::new`]: #method.new - #[stable(feature = "weak_counts", since = "1.41.0")] - pub fn strong_count(&self) -> usize { - if let Some(inner) = self.inner() { inner.strong() } else { 0 } - } - - /// Gets the number of `Weak` pointers pointing to this allocation. - /// - /// If no strong pointers remain, this will return zero. - #[stable(feature = "weak_counts", since = "1.41.0")] - pub fn weak_count(&self) -> usize { - self.inner() - .map(|inner| { - if inner.strong() > 0 { - inner.weak() - 1 // subtract the implicit weak ptr - } else { - 0 - } - }) - .unwrap_or(0) - } - - /// Returns `None` when the pointer is dangling and there is no allocated `RcBox` - /// (i.e., when this `Weak` was created by `Weak::new`). - #[inline] - fn inner(&self) -> Option<&RcBox<T>> { - if is_dangling(self.ptr) { None } else { Some(unsafe { self.ptr.as_ref() }) } - } - - /// Returns `true` if the two `Weak`s point to the same allocation (similar to - /// [`ptr::eq`]), or if both don't point to any allocation - /// (because they were created with `Weak::new()`). - /// - /// # Notes - /// - /// Since this compares pointers it means that `Weak::new()` will equal each - /// other, even though they don't point to any allocation. - /// - /// # Examples - /// - /// ``` - /// use std::rc::Rc; - /// - /// let first_rc = Rc::new(5); - /// let first = Rc::downgrade(&first_rc); - /// let second = Rc::downgrade(&first_rc); - /// - /// assert!(first.ptr_eq(&second)); - /// - /// let third_rc = Rc::new(5); - /// let third = Rc::downgrade(&third_rc); - /// - /// assert!(!first.ptr_eq(&third)); - /// ``` - /// - /// Comparing `Weak::new`. - /// - /// ``` - /// use std::rc::{Rc, Weak}; - /// - /// let first = Weak::new(); - /// let second = Weak::new(); - /// assert!(first.ptr_eq(&second)); - /// - /// let third_rc = Rc::new(()); - /// let third = Rc::downgrade(&third_rc); - /// assert!(!first.ptr_eq(&third)); - /// ``` - /// - /// [`ptr::eq`]: ../../std/ptr/fn.eq.html - #[inline] - #[stable(feature = "weak_ptr_eq", since = "1.39.0")] - pub fn ptr_eq(&self, other: &Self) -> bool { - self.ptr.as_ptr() == other.ptr.as_ptr() - } -} - -#[stable(feature = "rc_weak", since = "1.4.0")] -impl<T: ?Sized> Drop for Weak<T> { - /// Drops the `Weak` pointer. - /// - /// # Examples - /// - /// ``` - /// use std::rc::{Rc, Weak}; - /// - /// struct Foo; - /// - /// impl Drop for Foo { - /// fn drop(&mut self) { - /// println!("dropped!"); - /// } - /// } - /// - /// let foo = Rc::new(Foo); - /// let weak_foo = Rc::downgrade(&foo); - /// let other_weak_foo = Weak::clone(&weak_foo); - /// - /// drop(weak_foo); // Doesn't print anything - /// drop(foo); // Prints "dropped!" - /// - /// assert!(other_weak_foo.upgrade().is_none()); - /// ``` - fn drop(&mut self) { - if let Some(inner) = self.inner() { - inner.dec_weak(); - // the weak count starts at 1, and will only go to zero if all - // the strong pointers have disappeared. - if inner.weak() == 0 { - unsafe { - Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref())); - } - } - } - } -} - -#[stable(feature = "rc_weak", since = "1.4.0")] -impl<T: ?Sized> Clone for Weak<T> { - /// Makes a clone of the `Weak` pointer that points to the same allocation. - /// - /// # Examples - /// - /// ``` - /// use std::rc::{Rc, Weak}; - /// - /// let weak_five = Rc::downgrade(&Rc::new(5)); - /// - /// let _ = Weak::clone(&weak_five); - /// ``` - #[inline] - fn clone(&self) -> Weak<T> { - if let Some(inner) = self.inner() { - inner.inc_weak() - } - Weak { ptr: self.ptr } - } -} - -#[stable(feature = "rc_weak", since = "1.4.0")] -impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> { - fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - write!(f, "(Weak)") - } -} - -#[stable(feature = "downgraded_weak", since = "1.10.0")] -impl<T> Default for Weak<T> { - /// Constructs a new `Weak<T>`, allocating memory for `T` without initializing - /// it. Calling [`upgrade`] on the return value always gives [`None`]. - /// - /// [`None`]: ../../std/option/enum.Option.html - /// [`upgrade`]: ../../std/rc/struct.Weak.html#method.upgrade - /// - /// # Examples - /// - /// ``` - /// use std::rc::Weak; - /// - /// let empty: Weak<i64> = Default::default(); - /// assert!(empty.upgrade().is_none()); - /// ``` - fn default() -> Weak<T> { - Weak::new() - } -} - -// NOTE: We checked_add here to deal with mem::forget safely. In particular -// if you mem::forget Rcs (or Weaks), the ref-count can overflow, and then -// you can free the allocation while outstanding Rcs (or Weaks) exist. -// We abort because this is such a degenerate scenario that we don't care about -// what happens -- no real program should ever experience this. -// -// This should have negligible overhead since you don't actually need to -// clone these much in Rust thanks to ownership and move-semantics. - -#[doc(hidden)] -trait RcBoxPtr<T: ?Sized> { - fn inner(&self) -> &RcBox<T>; - - #[inline] - fn strong(&self) -> usize { - self.inner().strong.get() - } - - #[inline] - fn inc_strong(&self) { - let strong = self.strong(); - - // We want to abort on overflow instead of dropping the value. - // The reference count will never be zero when this is called; - // nevertheless, we insert an abort here to hint LLVM at - // an otherwise missed optimization. - if strong == 0 || strong == usize::MAX { - abort(); - } - self.inner().strong.set(strong + 1); - } - - #[inline] - fn dec_strong(&self) { - self.inner().strong.set(self.strong() - 1); - } - - #[inline] - fn weak(&self) -> usize { - self.inner().weak.get() - } - - #[inline] - fn inc_weak(&self) { - let weak = self.weak(); - - // We want to abort on overflow instead of dropping the value. - // The reference count will never be zero when this is called; - // nevertheless, we insert an abort here to hint LLVM at - // an otherwise missed optimization. - if weak == 0 || weak == usize::MAX { - abort(); - } - self.inner().weak.set(weak + 1); - } - - #[inline] - fn dec_weak(&self) { - self.inner().weak.set(self.weak() - 1); - } -} - -impl<T: ?Sized> RcBoxPtr<T> for Rc<T> { - #[inline(always)] - fn inner(&self) -> &RcBox<T> { - unsafe { self.ptr.as_ref() } - } -} - -impl<T: ?Sized> RcBoxPtr<T> for RcBox<T> { - #[inline(always)] - fn inner(&self) -> &RcBox<T> { - self - } -} - -#[stable(feature = "rust1", since = "1.0.0")] -impl<T: ?Sized> borrow::Borrow<T> for Rc<T> { - fn borrow(&self) -> &T { - &**self - } -} - -#[stable(since = "1.5.0", feature = "smart_ptr_as_ref")] -impl<T: ?Sized> AsRef<T> for Rc<T> { - fn as_ref(&self) -> &T { - &**self - } -} - -#[stable(feature = "pin", since = "1.33.0")] -impl<T: ?Sized> Unpin for Rc<T> {} - -/// Get the offset within an `ArcInner` for -/// a payload of type described by a pointer. -/// -/// # Safety -/// -/// This has the same safety requirements as `align_of_val_raw`. In effect: -/// -/// - This function is safe for any argument if `T` is sized, and -/// - if `T` is unsized, the pointer must have appropriate pointer metadata -/// aquired from the real instance that you are getting this offset for. -unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize { - // Align the unsized value to the end of the `RcBox`. - // Because it is ?Sized, it will always be the last field in memory. - // Note: This is a detail of the current implementation of the compiler, - // and is not a guaranteed language detail. Do not rely on it outside of std. - unsafe { data_offset_align(align_of_val_raw(ptr)) } -} - -#[inline] -fn data_offset_align(align: usize) -> isize { - let layout = Layout::new::<RcBox<()>>(); - (layout.size() + layout.padding_needed_for(align)) as isize -} |