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fuchsia / third_party / rust / c949d8ee69268c5c176c89834782b2654e0766ad / . / src / liballoc / rc.rs
blob: d3a55c59ff69c1e33917ef52c8dba8c9eb65acab [file] [log] [blame]
#![allow(deprecated)]
//! 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 value in the heap. When the last [`Rc`] pointer to a
//! given value is destroyed, the pointed-to value is also destroyed.
//!
//! 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 has
//! already been dropped.
//!
//! 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 value may have
//! already been destroyed.
//!
//! # Cloning references
//!
//! Creating a new reference from 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>`
//! // value gives us a new pointer to the same `Owner` value, 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>` values pointing at the same `Owner`, it will remain
//! // allocated. 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 between the values. This means that their
//! reference counts can never reach 0, and the values will remain allocated
//! forever: 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 value is still allocated, we need to call
//! // `upgrade`, which returns an `Option<Rc<Gadget>>`.
//! //
//! // In this case we know the value 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 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::fmt;
use core::hash::{Hash, Hasher};
use core::intrinsics::abort;
use core::marker;
use core::marker::{Unpin, Unsize, PhantomData};
use core::mem::{self, align_of_val, forget, size_of_val};
use core::ops::{Deref, Receiver};
use core::ops::{CoerceUnsized, DispatchFromDyn};
use core::pin::Pin;
use core::ptr::{self, NonNull};
use core::convert::From;
use core::usize;
use alloc::{Global, Alloc, Layout, box_free, handle_alloc_error};
use string::String;
use vec::Vec;
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), lang = "rc")]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Rc<T: ?Sized> {
ptr: NonNull<RcBox<T>>,
phantom: PhantomData<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 = "0")]
impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Rc<U>> for Rc<T> {}
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> {
Rc {
// 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.
ptr: Box::into_raw_non_null(box RcBox {
strong: Cell::new(1),
weak: Cell::new(1),
value,
}),
phantom: PhantomData,
}
}
/// 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 contained 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: ?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(10);
/// let x_ptr = Rc::into_raw(x);
/// assert_eq!(unsafe { *x_ptr }, 10);
/// ```
#[stable(feature = "rc_raw", since = "1.17.0")]
pub fn into_raw(this: Self) -> *const T {
let ptr: *const T = &*this;
mem::forget(this);
ptr
}
/// Constructs an `Rc` from a raw pointer.
///
/// The raw pointer must have been previously returned by a call to a
/// [`Rc::into_raw`][into_raw].
///
/// This function is unsafe because improper use may lead to memory problems. For example, a
/// double-free may occur if the function is called twice on the same raw pointer.
///
/// [into_raw]: struct.Rc.html#method.into_raw
///
/// # Examples
///
/// ```
/// use std::rc::Rc;
///
/// let x = Rc::new(10);
/// 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, 10);
///
/// // 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 {
// Align the unsized value to the end of the RcBox.
// Because it is ?Sized, it will always be the last field in memory.
let align = align_of_val(&*ptr);
let layout = Layout::new::<RcBox<()>>();
let offset = (layout.size() + layout.padding_needed_for(align)) as isize;
// Reverse the offset to find the original RcBox.
let fake_ptr = ptr as *mut RcBox<T>;
let rc_ptr = set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset));
Rc {
ptr: NonNull::new_unchecked(rc_ptr),
phantom: PhantomData,
}
}
/// Creates a new [`Weak`][weak] pointer to this value.
///
/// [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 value.
///
/// [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 value.
///
/// # 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 inner value.
///
/// [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 to the inner value, if there are
/// no other `Rc` or [`Weak`][weak] pointers to the same value.
///
/// 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 it's shared.
///
/// [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(&mut this.ptr.as_mut().value)
}
} else {
None
}
}
#[inline]
#[stable(feature = "ptr_eq", since = "1.17.0")]
/// Returns true if the two `Rc`s point to the same value (not
/// just values that compare as equal).
///
/// # 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));
/// ```
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` or [`Weak`][weak] pointers to the same value,
/// then `make_mut` will invoke [`clone`][clone] on the inner value to
/// ensure unique ownership. This is also referred to as clone-on-write.
///
/// See also [`get_mut`][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 values.
/// assert_eq!(*data, 8);
/// assert_eq!(*other_data, 12);
/// ```
#[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 inner value.
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);
/// }
/// }
///
/// fn main() {
/// 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 { ptr, phantom: PhantomData })
} else {
Err(self)
}
}
}
impl<T: ?Sized> Rc<T> {
// Allocates an `RcBox<T>` with sufficient space for an unsized value
unsafe fn allocate_for_ptr(ptr: *const T) -> *mut RcBox<T> {
// Calculate layout using the given value.
// 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(Layout::for_value(&*ptr)).unwrap().0
.pad_to_align().unwrap();
let mem = Global.alloc(layout)
.unwrap_or_else(|_| handle_alloc_error(layout));
// Initialize the RcBox
let inner = set_data_ptr(ptr as *mut T, mem.as_ptr() as *mut u8) as *mut RcBox<T>;
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
}
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);
Rc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
}
}
}
// 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 {
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]> {
let v_ptr = v as *const [T];
let ptr = Self::allocate_for_ptr(v_ptr);
ptr::copy_nonoverlapping(
v.as_ptr(),
&mut (*ptr).value as *mut [T] as *mut T,
v.len());
Rc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
}
}
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 {
// 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) {
use core::slice::from_raw_parts_mut;
unsafe {
let slice = from_raw_parts_mut(self.elems, self.n_elems);
ptr::drop_in_place(slice);
Global.dealloc(self.mem, self.layout.clone());
}
}
}
unsafe {
let v_ptr = v as *const [T];
let ptr = Self::allocate_for_ptr(v_ptr);
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: elems,
layout: layout,
n_elems: 0,
};
for (i, item) in v.iter().enumerate() {
ptr::write(elems.add(i), item.clone());
guard.n_elems += 1;
}
// All clear. Forget the guard so it doesn't free the new RcBox.
forget(guard);
Rc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
}
}
}
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 = "0")]
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 inner value, 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();
Rc { ptr: self.ptr, phantom: PhantomData }
}
}
#[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
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + Eq> 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.
///
/// If `T` also implements `Eq`, two `Rc`s that point to the same value 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`, two `Rc`s that point to the same value 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<'a, T: Clone> From<&'a [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<'a> From<&'a 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
}
}
}
/// `Weak` is a version of [`Rc`] that holds a non-owning reference to the
/// managed value. The value 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 inner value from being dropped, and `Weak` itself makes no
/// guarantees about the value still being present and may return [`None`]
/// when [`upgrade`]d.
///
/// A `Weak` pointer is useful for keeping a temporary reference to the value
/// within [`Rc`] without extending its lifetime. 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.
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 = "0")]
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"),
}
}
}
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`], extending
/// the lifetime of the value if successful.
///
/// Returns [`None`] if the 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 { ptr: self.ptr, phantom: PhantomData })
}
}
/// Return `None` when the pointer is dangling and there is no allocated `RcBox`,
/// i.e., 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 value (not just values
/// that compare as equal).
///
/// # Notes
///
/// Since this compares pointers it means that `Weak::new()` will equal each
/// other, even though they don't point to any value.
///
/// # Examples
///
/// ```
/// #![feature(weak_ptr_eq)]
/// use std::rc::{Rc, Weak};
///
/// let first_rc = Rc::new(5);
/// let first = Rc::downgrade(&first_rc);
/// let second = Rc::downgrade(&first_rc);
///
/// assert!(Weak::ptr_eq(&first, &second));
///
/// let third_rc = Rc::new(5);
/// let third = Rc::downgrade(&third_rc);
///
/// assert!(!Weak::ptr_eq(&first, &third));
/// ```
///
/// Comparing `Weak::new`.
///
/// ```
/// #![feature(weak_ptr_eq)]
/// use std::rc::{Rc, Weak};
///
/// let first = Weak::new();
/// let second = Weak::new();
/// assert!(Weak::ptr_eq(&first, &second));
///
/// let third_rc = Rc::new(());
/// let third = Rc::downgrade(&third_rc);
/// assert!(!Weak::ptr_eq(&first, &third));
/// ```
#[inline]
#[unstable(feature = "weak_ptr_eq", issue = "55981")]
pub fn ptr_eq(this: &Self, other: &Self) -> bool {
this.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 value.
///
/// # 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) {
// 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 self.strong() == 0 || self.strong() == usize::max_value() {
unsafe { abort(); }
}
self.inner().strong.set(self.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) {
// 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 self.weak() == 0 || self.weak() == usize::max_value() {
unsafe { abort(); }
}
self.inner().weak.set(self.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
}
}
#[cfg(test)]
mod tests {
use super::{Rc, Weak};
use std::boxed::Box;
use std::cell::RefCell;
use std::option::Option;
use std::option::Option::{None, Some};
use std::result::Result::{Err, Ok};
use std::mem::drop;
use std::clone::Clone;
use std::convert::From;
#[test]
fn test_clone() {
let x = Rc::new(RefCell::new(5));
let y = x.clone();
*x.borrow_mut() = 20;
assert_eq!(*y.borrow(), 20);
}
#[test]
fn test_simple() {
let x = Rc::new(5);
assert_eq!(*x, 5);
}
#[test]
fn test_simple_clone() {
let x = Rc::new(5);
let y = x.clone();
assert_eq!(*x, 5);
assert_eq!(*y, 5);
}
#[test]
fn test_destructor() {
let x: Rc<Box<_>> = Rc::new(box 5);
assert_eq!(**x, 5);
}
#[test]
fn test_live() {
let x = Rc::new(5);
let y = Rc::downgrade(&x);
assert!(y.upgrade().is_some());
}
#[test]
fn test_dead() {
let x = Rc::new(5);
let y = Rc::downgrade(&x);
drop(x);
assert!(y.upgrade().is_none());
}
#[test]
fn weak_self_cyclic() {
struct Cycle {
x: RefCell<Option<Weak<Cycle>>>,
}
let a = Rc::new(Cycle { x: RefCell::new(None) });
let b = Rc::downgrade(&a.clone());
*a.x.borrow_mut() = Some(b);
// hopefully we don't double-free (or leak)...
}
#[test]
fn is_unique() {
let x = Rc::new(3);
assert!(Rc::is_unique(&x));
let y = x.clone();
assert!(!Rc::is_unique(&x));
drop(y);
assert!(Rc::is_unique(&x));
let w = Rc::downgrade(&x);
assert!(!Rc::is_unique(&x));
drop(w);
assert!(Rc::is_unique(&x));
}
#[test]
fn test_strong_count() {
let a = Rc::new(0);
assert!(Rc::strong_count(&a) == 1);
let w = Rc::downgrade(&a);
assert!(Rc::strong_count(&a) == 1);
let b = w.upgrade().expect("upgrade of live rc failed");
assert!(Rc::strong_count(&b) == 2);
assert!(Rc::strong_count(&a) == 2);
drop(w);
drop(a);
assert!(Rc::strong_count(&b) == 1);
let c = b.clone();
assert!(Rc::strong_count(&b) == 2);
assert!(Rc::strong_count(&c) == 2);
}
#[test]
fn test_weak_count() {
let a = Rc::new(0);
assert!(Rc::strong_count(&a) == 1);
assert!(Rc::weak_count(&a) == 0);
let w = Rc::downgrade(&a);
assert!(Rc::strong_count(&a) == 1);
assert!(Rc::weak_count(&a) == 1);
drop(w);
assert!(Rc::strong_count(&a) == 1);
assert!(Rc::weak_count(&a) == 0);
let c = a.clone();
assert!(Rc::strong_count(&a) == 2);
assert!(Rc::weak_count(&a) == 0);
drop(c);
}
#[test]
fn try_unwrap() {
let x = Rc::new(3);
assert_eq!(Rc::try_unwrap(x), Ok(3));
let x = Rc::new(4);
let _y = x.clone();
assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4)));
let x = Rc::new(5);
let _w = Rc::downgrade(&x);
assert_eq!(Rc::try_unwrap(x), Ok(5));
}
#[test]
fn into_from_raw() {
let x = Rc::new(box "hello");
let y = x.clone();
let x_ptr = Rc::into_raw(x);
drop(y);
unsafe {
assert_eq!(**x_ptr, "hello");
let x = Rc::from_raw(x_ptr);
assert_eq!(**x, "hello");
assert_eq!(Rc::try_unwrap(x).map(|x| *x), Ok("hello"));
}
}
#[test]
fn test_into_from_raw_unsized() {
use std::fmt::Display;
use std::string::ToString;
let rc: Rc<str> = Rc::from("foo");
let ptr = Rc::into_raw(rc.clone());
let rc2 = unsafe { Rc::from_raw(ptr) };
assert_eq!(unsafe { &*ptr }, "foo");
assert_eq!(rc, rc2);
let rc: Rc<dyn Display> = Rc::new(123);
let ptr = Rc::into_raw(rc.clone());
let rc2 = unsafe { Rc::from_raw(ptr) };
assert_eq!(unsafe { &*ptr }.to_string(), "123");
assert_eq!(rc2.to_string(), "123");
}
#[test]
fn get_mut() {
let mut x = Rc::new(3);
*Rc::get_mut(&mut x).unwrap() = 4;
assert_eq!(*x, 4);
let y = x.clone();
assert!(Rc::get_mut(&mut x).is_none());
drop(y);
assert!(Rc::get_mut(&mut x).is_some());
let _w = Rc::downgrade(&x);
assert!(Rc::get_mut(&mut x).is_none());
}
#[test]
fn test_cowrc_clone_make_unique() {
let mut cow0 = Rc::new(75);
let mut cow1 = cow0.clone();
let mut cow2 = cow1.clone();
assert!(75 == *Rc::make_mut(&mut cow0));
assert!(75 == *Rc::make_mut(&mut cow1));
assert!(75 == *Rc::make_mut(&mut cow2));
*Rc::make_mut(&mut cow0) += 1;
*Rc::make_mut(&mut cow1) += 2;
*Rc::make_mut(&mut cow2) += 3;
assert!(76 == *cow0);
assert!(77 == *cow1);
assert!(78 == *cow2);
// none should point to the same backing memory
assert!(*cow0 != *cow1);
assert!(*cow0 != *cow2);
assert!(*cow1 != *cow2);
}
#[test]
fn test_cowrc_clone_unique2() {
let mut cow0 = Rc::new(75);
let cow1 = cow0.clone();
let cow2 = cow1.clone();
assert!(75 == *cow0);
assert!(75 == *cow1);
assert!(75 == *cow2);
*Rc::make_mut(&mut cow0) += 1;
assert!(76 == *cow0);
assert!(75 == *cow1);
assert!(75 == *cow2);
// cow1 and cow2 should share the same contents
// cow0 should have a unique reference
assert!(*cow0 != *cow1);
assert!(*cow0 != *cow2);
assert!(*cow1 == *cow2);
}
#[test]
fn test_cowrc_clone_weak() {
let mut cow0 = Rc::new(75);
let cow1_weak = Rc::downgrade(&cow0);
assert!(75 == *cow0);
assert!(75 == *cow1_weak.upgrade().unwrap());
*Rc::make_mut(&mut cow0) += 1;
assert!(76 == *cow0);
assert!(cow1_weak.upgrade().is_none());
}
#[test]
fn test_show() {
let foo = Rc::new(75);
assert_eq!(format!("{:?}", foo), "75");
}
#[test]
fn test_unsized() {
let foo: Rc<[i32]> = Rc::new([1, 2, 3]);
assert_eq!(foo, foo.clone());
}
#[test]
fn test_from_owned() {
let foo = 123;
let foo_rc = Rc::from(foo);
assert!(123 == *foo_rc);
}
#[test]
fn test_new_weak() {
let foo: Weak<usize> = Weak::new();
assert!(foo.upgrade().is_none());
}
#[test]
fn test_ptr_eq() {
let five = Rc::new(5);
let same_five = five.clone();
let other_five = Rc::new(5);
assert!(Rc::ptr_eq(&five, &same_five));
assert!(!Rc::ptr_eq(&five, &other_five));
}
#[test]
fn test_from_str() {
let r: Rc<str> = Rc::from("foo");
assert_eq!(&r[..], "foo");
}
#[test]
fn test_copy_from_slice() {
let s: &[u32] = &[1, 2, 3];
let r: Rc<[u32]> = Rc::from(s);
assert_eq!(&r[..], [1, 2, 3]);
}
#[test]
fn test_clone_from_slice() {
#[derive(Clone, Debug, Eq, PartialEq)]
struct X(u32);
let s: &[X] = &[X(1), X(2), X(3)];
let r: Rc<[X]> = Rc::from(s);
assert_eq!(&r[..], s);
}
#[test]
#[should_panic]
fn test_clone_from_slice_panic() {
use std::string::{String, ToString};
struct Fail(u32, String);
impl Clone for Fail {
fn clone(&self) -> Fail {
if self.0 == 2 {
panic!();
}
Fail(self.0, self.1.clone())
}
}
let s: &[Fail] = &[
Fail(0, "foo".to_string()),
Fail(1, "bar".to_string()),
Fail(2, "baz".to_string()),
];
// Should panic, but not cause memory corruption
let _r: Rc<[Fail]> = Rc::from(s);
}
#[test]
fn test_from_box() {
let b: Box<u32> = box 123;
let r: Rc<u32> = Rc::from(b);
assert_eq!(*r, 123);
}
#[test]
fn test_from_box_str() {
use std::string::String;
let s = String::from("foo").into_boxed_str();
let r: Rc<str> = Rc::from(s);
assert_eq!(&r[..], "foo");
}
#[test]
fn test_from_box_slice() {
let s = vec![1, 2, 3].into_boxed_slice();
let r: Rc<[u32]> = Rc::from(s);
assert_eq!(&r[..], [1, 2, 3]);
}
#[test]
fn test_from_box_trait() {
use std::fmt::Display;
use std::string::ToString;
let b: Box<dyn Display> = box 123;
let r: Rc<dyn Display> = Rc::from(b);
assert_eq!(r.to_string(), "123");
}
#[test]
fn test_from_box_trait_zero_sized() {
use std::fmt::Debug;
let b: Box<dyn Debug> = box ();
let r: Rc<dyn Debug> = Rc::from(b);
assert_eq!(format!("{:?}", r), "()");
}
#[test]
fn test_from_vec() {
let v = vec![1, 2, 3];
let r: Rc<[u32]> = Rc::from(v);
assert_eq!(&r[..], [1, 2, 3]);
}
#[test]
fn test_downcast() {
use std::any::Any;
let r1: Rc<dyn Any> = Rc::new(i32::max_value());
let r2: Rc<dyn Any> = Rc::new("abc");
assert!(r1.clone().downcast::<u32>().is_err());
let r1i32 = r1.downcast::<i32>();
assert!(r1i32.is_ok());
assert_eq!(r1i32.unwrap(), Rc::new(i32::max_value()));
assert!(r2.clone().downcast::<i32>().is_err());
let r2str = r2.downcast::<&'static str>();
assert!(r2str.is_ok());
assert_eq!(r2str.unwrap(), Rc::new("abc"));
}
}
#[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> { }