#![allow(deprecated)]
-//! Single-threaded reference-counting pointers.
+//! 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
+//! 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 obtain a mutable reference to
+//! 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].
//! 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
+//! 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.
//! [`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`.
//! // the reference count in the process.
//! let gadget1 = Gadget {
//! id: 1,
-//! owner: gadget_owner.clone(),
+//! owner: Rc::clone(&gadget_owner),
//! };
//! let gadget2 = Gadget {
//! id: 2,
-//! owner: gadget_owner.clone(),
+//! owner: Rc::clone(&gadget_owner),
//! };
//!
//! // Dispose of our local variable `gadget_owner`.
//! let gadget1 = Rc::new(
//! Gadget {
//! id: 1,
-//! owner: gadget_owner.clone(),
+//! owner: Rc::clone(&gadget_owner),
//! }
//! );
//! let gadget2 = Rc::new(
//! Gadget {
//! id: 2,
-//! owner: gadget_owner.clone(),
+//! owner: Rc::clone(&gadget_owner),
//! }
//! );
//!
//! [downgrade]: struct.Rc.html#method.downgrade
//! [upgrade]: struct.Weak.html#method.upgrade
//! [`None`]: ../../std/option/enum.Option.html#variant.None
-//! [assoc]: ../../book/method-syntax.html#associated-functions
+//! [assoc]: ../../book/first-edition/method-syntax.html#associated-functions
//! [mutability]: ../../std/cell/index.html#introducing-mutability-inside-of-something-immutable
#![stable(feature = "rust1", since = "1.0.0")]
#[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, assume};
+use core::intrinsics::abort;
use core::marker;
-use core::marker::Unsize;
-use core::mem::{self, align_of_val, forget, size_of, size_of_val, uninitialized};
+use core::marker::{Unsize, PhantomData};
+use core::mem::{self, align_of_val, forget, size_of_val, uninitialized};
use core::ops::Deref;
use core::ops::CoerceUnsized;
-use core::ptr::{self, Shared};
+use core::ptr::{self, NonNull};
use core::convert::From;
-use heap::deallocate;
-use raw_vec::RawVec;
+use heap::{Heap, Alloc, Layout, box_free};
+use string::String;
+use vec::Vec;
struct RcBox<T: ?Sized> {
strong: Cell<usize>,
value: T,
}
-
-/// A single-threaded reference-counting pointer.
+/// 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(&value)`][get_mut] instead of
+/// 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
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Rc<T: ?Sized> {
- ptr: Shared<RcBox<T>>,
+ ptr: NonNull<RcBox<T>>,
+ phantom: PhantomData<T>,
}
#[stable(feature = "rust1", since = "1.0.0")]
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn new(value: T) -> Rc<T> {
- unsafe {
- 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: Shared::new(Box::into_raw(box RcBox {
- strong: Cell::new(1),
- weak: Cell::new(1),
- value: value,
- })),
- }
+ 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,
}
}
/// assert_eq!(Rc::try_unwrap(x), Ok(3));
///
/// let x = Rc::new(4);
- /// let _y = x.clone();
+ /// let _y = Rc::clone(&x);
/// assert_eq!(*Rc::try_unwrap(x).unwrap_err(), 4);
/// ```
#[inline]
unsafe {
let val = ptr::read(&*this); // copy the contained object
- // Indicate to Weaks that they can't be promoted by decrememting
+ // 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.
Err(this)
}
}
+}
- /// Checks whether [`Rc::try_unwrap`][try_unwrap] would return
- /// [`Ok`].
- ///
- /// [try_unwrap]: struct.Rc.html#method.try_unwrap
- /// [`Ok`]: ../../std/result/enum.Result.html#variant.Ok
- #[unstable(feature = "rc_would_unwrap",
- reason = "just added for niche usecase",
- issue = "28356")]
- #[rustc_deprecated(since = "1.15.0", reason = "too niche; use `strong_count` instead")]
- pub fn would_unwrap(this: &Self) -> bool {
- Rc::strong_count(&this) == 1
- }
-
+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
/// ```
#[stable(feature = "rc_raw", since = "1.17.0")]
pub fn into_raw(this: Self) -> *const T {
- let ptr = unsafe { &mut (*this.ptr.as_mut_ptr()).value as *const _ };
+ let ptr: *const T = &*this;
mem::forget(this);
ptr
}
/// ```
#[stable(feature = "rc_raw", since = "1.17.0")]
pub unsafe fn from_raw(ptr: *const T) -> Self {
- // To find the corresponding pointer to the `RcBox` we need to subtract the offset of the
- // `value` field from the pointer.
- Rc { ptr: Shared::new((ptr as *const u8).offset(-offset_of!(RcBox<T>, value)) as *const _) }
- }
-}
-
-impl Rc<str> {
- /// Constructs a new `Rc<str>` from a string slice.
- #[doc(hidden)]
- #[unstable(feature = "rustc_private",
- reason = "for internal use in rustc",
- issue = "0")]
- pub fn __from_str(value: &str) -> Rc<str> {
- unsafe {
- // Allocate enough space for `RcBox<str>`.
- let aligned_len = 2 + (value.len() + size_of::<usize>() - 1) / size_of::<usize>();
- let vec = RawVec::<usize>::with_capacity(aligned_len);
- let ptr = vec.ptr();
- forget(vec);
- // Initialize fields of `RcBox<str>`.
- *ptr.offset(0) = 1; // strong: Cell::new(1)
- *ptr.offset(1) = 1; // weak: Cell::new(1)
- ptr::copy_nonoverlapping(value.as_ptr(), ptr.offset(2) as *mut u8, value.len());
- // Combine the allocation address and the string length into a fat pointer to `RcBox`.
- let rcbox_ptr: *mut RcBox<str> = mem::transmute([ptr as usize, value.len()]);
- assert!(aligned_len * size_of::<usize>() == size_of_val(&*rcbox_ptr));
- Rc { ptr: Shared::new(rcbox_ptr) }
+ // 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,
}
}
-}
-impl<T: ?Sized> Rc<T> {
/// Creates a new [`Weak`][weak] pointer to this value.
///
/// [weak]: struct.Weak.html
/// use std::rc::Rc;
///
/// let five = Rc::new(5);
- /// let _also_five = five.clone();
+ /// let _also_five = Rc::clone(&five);
///
/// assert_eq!(2, Rc::strong_count(&five));
/// ```
///
/// [weak]: struct.Weak.html
#[inline]
- #[unstable(feature = "is_unique", reason = "uniqueness has unclear meaning",
- issue = "28356")]
- #[rustc_deprecated(since = "1.15.0",
- reason = "too niche; use `strong_count` and `weak_count` instead")]
- pub fn is_unique(this: &Self) -> bool {
+ fn is_unique(this: &Self) -> bool {
Rc::weak_count(this) == 0 && Rc::strong_count(this) == 1
}
/// *Rc::get_mut(&mut x).unwrap() = 4;
/// assert_eq!(*x, 4);
///
- /// let _y = x.clone();
+ /// 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) {
- let inner = unsafe { &mut *this.ptr.as_mut_ptr() };
- Some(&mut inner.value)
+ unsafe {
+ Some(&mut this.ptr.as_mut().value)
+ }
} else {
None
}
/// use std::rc::Rc;
///
/// let five = Rc::new(5);
- /// let same_five = five.clone();
+ /// 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 {
- let this_ptr: *const RcBox<T> = *this.ptr;
- let other_ptr: *const RcBox<T> = *other.ptr;
- this_ptr == other_ptr
+ this.ptr.as_ptr() == other.ptr.as_ptr()
}
}
/// let mut data = Rc::new(5);
///
/// *Rc::make_mut(&mut data) += 1; // Won't clone anything
- /// let mut other_data = data.clone(); // Won't clone inner data
+ /// 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
} 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).value));
+ 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
// 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.
- let inner = unsafe { &mut *this.ptr.as_mut_ptr() };
- &mut inner.value
+ unsafe {
+ &mut this.ptr.as_mut().value
+ }
+ }
+}
+
+impl Rc<Any> {
+ #[inline]
+ #[unstable(feature = "rc_downcast", issue = "44608")]
+ /// Attempt to downcast the `Rc<Any>` to a concrete type.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// #![feature(rc_downcast)]
+ /// use std::any::Any;
+ /// use std::rc::Rc;
+ ///
+ /// fn print_if_string(value: Rc<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<Any>> {
+ if (*self).is::<T>() {
+ // avoid the pointer arithmetic in from_raw
+ unsafe {
+ let raw: *const RcBox<Any> = self.ptr.as_ptr();
+ forget(self);
+ Ok(Rc {
+ ptr: NonNull::new_unchecked(raw as *const RcBox<T> as *mut _),
+ 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> {
+ // Create a fake RcBox to find allocation size and alignment
+ let fake_ptr = ptr as *mut RcBox<T>;
+
+ let layout = Layout::for_value(&*fake_ptr);
+
+ let mem = Heap.alloc(layout)
+ .unwrap_or_else(|e| Heap.oom(e));
+
+ // Initialize the real RcBox
+ let inner = set_data_ptr(ptr as *mut T, mem) as *mut RcBox<T>;
+
+ 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 bptr = Box::into_raw(v);
+
+ 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(bptr);
+
+ 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: *mut 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);
+
+ Heap.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: mem,
+ elems: elems,
+ layout: layout,
+ n_elems: 0,
+ };
+
+ for (i, item) in v.iter().enumerate() {
+ ptr::write(elems.offset(i as isize), 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) }
}
}
/// }
///
/// let foo = Rc::new(Foo);
- /// let foo2 = foo.clone();
+ /// let foo2 = Rc::clone(&foo);
///
/// drop(foo); // Doesn't print anything
/// drop(foo2); // Prints "dropped!"
/// ```
fn drop(&mut self) {
unsafe {
- let ptr = self.ptr.as_mut_ptr();
+ let ptr = self.ptr.as_ptr();
self.dec_strong();
if self.strong() == 0 {
// destroy the contained object
- ptr::drop_in_place(&mut (*ptr).value);
+ 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 {
- deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
+ Heap.dealloc(ptr as *mut u8, Layout::for_value(&*ptr));
}
}
}
///
/// let five = Rc::new(5);
///
- /// five.clone();
+ /// Rc::clone(&five);
/// ```
#[inline]
fn clone(&self) -> Rc<T> {
self.inc_strong();
- Rc { ptr: self.ptr }
+ Rc { ptr: self.ptr, phantom: PhantomData }
}
}
#[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.ptr, f)
+ fmt::Pointer::fmt(&(&**self as *const T), f)
}
}
}
}
-/// A weak version of [`Rc`][rc].
+#[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>>`.
///
-/// `Weak` pointers do not count towards determining if the inner value
-/// should be dropped.
+/// 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.
///
-/// The typical way to obtain a `Weak` pointer is to call
-/// [`Rc::downgrade`][downgrade].
+/// 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.
///
-/// See the [module-level documentation](./index.html) for more details.
+/// The typical way to obtain a `Weak` pointer is to call [`Rc::downgrade`].
///
-/// [rc]: struct.Rc.html
-/// [downgrade]: struct.Rc.html#method.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> {
- ptr: Shared<RcBox<T>>,
+ ptr: NonNull<RcBox<T>>,
}
#[stable(feature = "rc_weak", since = "1.4.0")]
impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {}
impl<T> Weak<T> {
- /// Constructs a new `Weak<T>`, without an accompanying instance of `T`.
- ///
- /// This allocates memory for `T`, but does not initialize it. Calling
- /// [`upgrade`][upgrade] on the return value always gives
- /// [`None`][option].
+ /// Constructs a new `Weak<T>`, allocating memory for `T` without initializing
+ /// it. Calling [`upgrade`] on the return value always gives [`None`].
///
- /// [upgrade]: struct.Weak.html#method.upgrade
- /// [option]: ../../std/option/enum.Option.html
+ /// [`upgrade`]: struct.Weak.html#method.upgrade
+ /// [`None`]: ../../std/option/enum.Option.html
///
/// # Examples
///
pub fn new() -> Weak<T> {
unsafe {
Weak {
- ptr: Shared::new(Box::into_raw(box RcBox {
+ ptr: Box::into_raw_non_null(box RcBox {
strong: Cell::new(0),
weak: Cell::new(1),
value: uninitialized(),
- })),
+ }),
}
}
}
}
impl<T: ?Sized> Weak<T> {
- /// Upgrades the `Weak` pointer to an [`Rc`][rc], if possible.
+ /// Attempts to upgrade the `Weak` pointer to an [`Rc`], extending
+ /// the lifetime of the value if successful.
///
- /// Returns [`None`][option] if the strong count has reached zero and the
- /// inner value was destroyed.
+ /// Returns [`None`] if the value has since been dropped.
///
- /// [rc]: struct.Rc.html
- /// [option]: ../../std/option/enum.Option.html
+ /// [`Rc`]: struct.Rc.html
+ /// [`None`]: ../../std/option/enum.Option.html
///
/// # Examples
///
None
} else {
self.inc_strong();
- Some(Rc { ptr: self.ptr })
+ Some(Rc { ptr: self.ptr, phantom: PhantomData })
}
}
}
impl<T: ?Sized> Drop for Weak<T> {
/// Drops the `Weak` pointer.
///
- /// This will decrement the weak reference count.
- ///
/// # Examples
///
/// ```
- /// use std::rc::Rc;
+ /// use std::rc::{Rc, Weak};
///
/// struct Foo;
///
///
/// let foo = Rc::new(Foo);
/// let weak_foo = Rc::downgrade(&foo);
- /// let other_weak_foo = weak_foo.clone();
+ /// let other_weak_foo = Weak::clone(&weak_foo);
///
/// drop(weak_foo); // Doesn't print anything
/// drop(foo); // Prints "dropped!"
/// ```
fn drop(&mut self) {
unsafe {
- let ptr = *self.ptr;
+ let ptr = self.ptr.as_ptr();
self.dec_weak();
// the weak count starts at 1, and will only go to zero if all
// the strong pointers have disappeared.
if self.weak() == 0 {
- deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
+ Heap.dealloc(ptr as *mut u8, Layout::for_value(&*ptr));
}
}
}
#[stable(feature = "rc_weak", since = "1.4.0")]
impl<T: ?Sized> Clone for Weak<T> {
- /// Makes a clone of the `Weak` pointer.
- ///
- /// This creates another pointer to the same inner value, increasing the
- /// weak reference count.
+ /// Makes a clone of the `Weak` pointer that points to the same value.
///
/// # Examples
///
/// ```
- /// use std::rc::Rc;
+ /// use std::rc::{Rc, Weak};
///
/// let weak_five = Rc::downgrade(&Rc::new(5));
///
- /// weak_five.clone();
+ /// Weak::clone(&weak_five);
/// ```
#[inline]
fn clone(&self) -> Weak<T> {
#[stable(feature = "downgraded_weak", since = "1.10.0")]
impl<T> Default for Weak<T> {
- /// Constructs a new `Weak<T>`, without an accompanying instance of `T`.
- ///
- /// This allocates memory for `T`, but does not initialize it. Calling
- /// [`upgrade`][upgrade] on the return value always gives
- /// [`None`][option].
+ /// Constructs a new `Weak<T>`, allocating memory for `T` without initializing
+ /// it. Calling [`upgrade`] on the return value always gives [`None`].
///
- /// [upgrade]: struct.Weak.html#method.upgrade
- /// [option]: ../../std/option/enum.Option.html
+ /// [`upgrade`]: struct.Weak.html#method.upgrade
+ /// [`None`]: ../../std/option/enum.Option.html
///
/// # Examples
///
#[inline(always)]
fn inner(&self) -> &RcBox<T> {
unsafe {
- // Safe to assume this here, as if it weren't true, we'd be breaking
- // the contract anyway.
- // This allows the null check to be elided in the destructor if we
- // manipulated the reference count in the same function.
- assume(!(*(&self.ptr as *const _ as *const *const ())).is_null());
- &(**self.ptr)
+ self.ptr.as_ref()
}
}
}
#[inline(always)]
fn inner(&self) -> &RcBox<T> {
unsafe {
- // Safe to assume this here, as if it weren't true, we'd be breaking
- // the contract anyway.
- // This allows the null check to be elided in the destructor if we
- // manipulated the reference count in the same function.
- assume(!(*(&self.ptr as *const _ as *const *const ())).is_null());
- &(**self.ptr)
+ self.ptr.as_ref()
}
}
}
}
}
+ #[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<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);
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<Display> = box 123;
+ let r: Rc<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<Debug> = box ();
+ let r: Rc<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<Any> = Rc::new(i32::max_value());
+ let r2: Rc<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")]
projects / rustc.git / blobdiff