| // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| //! Shareable mutable containers. |
| //! |
| //! Values of the `Cell<T>` and `RefCell<T>` types may be mutated through shared references (i.e. |
| //! the common `&T` type), whereas most Rust types can only be mutated through unique (`&mut T`) |
| //! references. We say that `Cell<T>` and `RefCell<T>` provide 'interior mutability', in contrast |
| //! with typical Rust types that exhibit 'inherited mutability'. |
| //! |
| //! Cell types come in two flavors: `Cell<T>` and `RefCell<T>`. `Cell<T>` provides `get` and `set` |
| //! methods that change the interior value with a single method call. `Cell<T>` though is only |
| //! compatible with types that implement `Copy`. For other types, one must use the `RefCell<T>` |
| //! type, acquiring a write lock before mutating. |
| //! |
| //! `RefCell<T>` uses Rust's lifetimes to implement 'dynamic borrowing', a process whereby one can |
| //! claim temporary, exclusive, mutable access to the inner value. Borrows for `RefCell<T>`s are |
| //! tracked 'at runtime', unlike Rust's native reference types which are entirely tracked |
| //! statically, at compile time. Because `RefCell<T>` borrows are dynamic it is possible to attempt |
| //! to borrow a value that is already mutably borrowed; when this happens it results in thread |
| //! panic. |
| //! |
| //! # When to choose interior mutability |
| //! |
| //! The more common inherited mutability, where one must have unique access to mutate a value, is |
| //! one of the key language elements that enables Rust to reason strongly about pointer aliasing, |
| //! statically preventing crash bugs. Because of that, inherited mutability is preferred, and |
| //! interior mutability is something of a last resort. Since cell types enable mutation where it |
| //! would otherwise be disallowed though, there are occasions when interior mutability might be |
| //! appropriate, or even *must* be used, e.g. |
| //! |
| //! * Introducing mutability 'inside' of something immutable |
| //! * Implementation details of logically-immutable methods. |
| //! * Mutating implementations of `Clone`. |
| //! |
| //! ## Introducing mutability 'inside' of something immutable |
| //! |
| //! Many shared smart pointer types, including `Rc<T>` and `Arc<T>`, provide containers that can be |
| //! cloned and shared between multiple parties. Because the contained values may be |
| //! multiply-aliased, they can only be borrowed with `&`, not `&mut`. Without cells it would be |
| //! impossible to mutate data inside of these smart pointers at all. |
| //! |
| //! It's very common then to put a `RefCell<T>` inside shared pointer types to reintroduce |
| //! mutability: |
| //! |
| //! ``` |
| //! use std::collections::HashMap; |
| //! use std::cell::RefCell; |
| //! use std::rc::Rc; |
| //! |
| //! fn main() { |
| //! let shared_map: Rc<RefCell<_>> = Rc::new(RefCell::new(HashMap::new())); |
| //! shared_map.borrow_mut().insert("africa", 92388); |
| //! shared_map.borrow_mut().insert("kyoto", 11837); |
| //! shared_map.borrow_mut().insert("piccadilly", 11826); |
| //! shared_map.borrow_mut().insert("marbles", 38); |
| //! } |
| //! ``` |
| //! |
| //! Note that this example uses `Rc<T>` and not `Arc<T>`. `RefCell<T>`s are for single-threaded |
| //! scenarios. Consider using `RwLock<T>` or `Mutex<T>` if you need shared mutability in a |
| //! multi-threaded situation. |
| //! |
| //! ## Implementation details of logically-immutable methods |
| //! |
| //! Occasionally it may be desirable not to expose in an API that there is mutation happening |
| //! "under the hood". This may be because logically the operation is immutable, but e.g. caching |
| //! forces the implementation to perform mutation; or because you must employ mutation to implement |
| //! a trait method that was originally defined to take `&self`. |
| //! |
| //! ``` |
| //! # #![allow(dead_code)] |
| //! use std::cell::RefCell; |
| //! |
| //! struct Graph { |
| //! edges: Vec<(i32, i32)>, |
| //! span_tree_cache: RefCell<Option<Vec<(i32, i32)>>> |
| //! } |
| //! |
| //! impl Graph { |
| //! fn minimum_spanning_tree(&self) -> Vec<(i32, i32)> { |
| //! // Create a new scope to contain the lifetime of the |
| //! // dynamic borrow |
| //! { |
| //! // Take a reference to the inside of cache cell |
| //! let mut cache = self.span_tree_cache.borrow_mut(); |
| //! if cache.is_some() { |
| //! return cache.as_ref().unwrap().clone(); |
| //! } |
| //! |
| //! let span_tree = self.calc_span_tree(); |
| //! *cache = Some(span_tree); |
| //! } |
| //! |
| //! // Recursive call to return the just-cached value. |
| //! // Note that if we had not let the previous borrow |
| //! // of the cache fall out of scope then the subsequent |
| //! // recursive borrow would cause a dynamic thread panic. |
| //! // This is the major hazard of using `RefCell`. |
| //! self.minimum_spanning_tree() |
| //! } |
| //! # fn calc_span_tree(&self) -> Vec<(i32, i32)> { vec![] } |
| //! } |
| //! ``` |
| //! |
| //! ## Mutating implementations of `Clone` |
| //! |
| //! This is simply a special - but common - case of the previous: hiding mutability for operations |
| //! that appear to be immutable. The `clone` method is expected to not change the source value, and |
| //! is declared to take `&self`, not `&mut self`. Therefore any mutation that happens in the |
| //! `clone` method must use cell types. For example, `Rc<T>` maintains its reference counts within a |
| //! `Cell<T>`. |
| //! |
| //! ``` |
| //! use std::cell::Cell; |
| //! |
| //! struct Rc<T> { |
| //! ptr: *mut RcBox<T> |
| //! } |
| //! |
| //! struct RcBox<T> { |
| //! # #[allow(dead_code)] |
| //! value: T, |
| //! refcount: Cell<usize> |
| //! } |
| //! |
| //! impl<T> Clone for Rc<T> { |
| //! fn clone(&self) -> Rc<T> { |
| //! unsafe { |
| //! (*self.ptr).refcount.set((*self.ptr).refcount.get() + 1); |
| //! Rc { ptr: self.ptr } |
| //! } |
| //! } |
| //! } |
| //! ``` |
| //! |
| |
| #![stable(feature = "rust1", since = "1.0.0")] |
| |
| use clone::Clone; |
| use cmp::{PartialEq, Eq}; |
| use default::Default; |
| use marker::{Copy, Send, Sync, Sized}; |
| use ops::{Deref, DerefMut, Drop, FnOnce}; |
| use option::Option; |
| use option::Option::{None, Some}; |
| |
| /// A mutable memory location that admits only `Copy` data. |
| /// |
| /// See the [module-level documentation](index.html) for more. |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub struct Cell<T> { |
| value: UnsafeCell<T>, |
| } |
| |
| impl<T:Copy> Cell<T> { |
| /// Creates a new `Cell` containing the given value. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cell::Cell; |
| /// |
| /// let c = Cell::new(5); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub const fn new(value: T) -> Cell<T> { |
| Cell { |
| value: UnsafeCell::new(value), |
| } |
| } |
| |
| /// Returns a copy of the contained value. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cell::Cell; |
| /// |
| /// let c = Cell::new(5); |
| /// |
| /// let five = c.get(); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn get(&self) -> T { |
| unsafe{ *self.value.get() } |
| } |
| |
| /// Sets the contained value. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cell::Cell; |
| /// |
| /// let c = Cell::new(5); |
| /// |
| /// c.set(10); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn set(&self, value: T) { |
| unsafe { |
| *self.value.get() = value; |
| } |
| } |
| |
| /// Returns a reference to the underlying `UnsafeCell`. |
| /// |
| /// # Safety |
| /// |
| /// This function is `unsafe` because `UnsafeCell`'s field is public. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(as_unsafe_cell)] |
| /// |
| /// use std::cell::Cell; |
| /// |
| /// let c = Cell::new(5); |
| /// |
| /// let uc = unsafe { c.as_unsafe_cell() }; |
| /// ``` |
| #[inline] |
| #[unstable(feature = "as_unsafe_cell", issue = "27708")] |
| pub unsafe fn as_unsafe_cell(&self) -> &UnsafeCell<T> { |
| &self.value |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| unsafe impl<T> Send for Cell<T> where T: Send {} |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T:Copy> Clone for Cell<T> { |
| #[inline] |
| fn clone(&self) -> Cell<T> { |
| Cell::new(self.get()) |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T:Default + Copy> Default for Cell<T> { |
| #[inline] |
| fn default() -> Cell<T> { |
| Cell::new(Default::default()) |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T:PartialEq + Copy> PartialEq for Cell<T> { |
| #[inline] |
| fn eq(&self, other: &Cell<T>) -> bool { |
| self.get() == other.get() |
| } |
| } |
| |
| #[stable(feature = "cell_eq", since = "1.2.0")] |
| impl<T:Eq + Copy> Eq for Cell<T> {} |
| |
| /// A mutable memory location with dynamically checked borrow rules |
| /// |
| /// See the [module-level documentation](index.html) for more. |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub struct RefCell<T: ?Sized> { |
| borrow: Cell<BorrowFlag>, |
| value: UnsafeCell<T>, |
| } |
| |
| /// An enumeration of values returned from the `state` method on a `RefCell<T>`. |
| #[derive(Copy, Clone, PartialEq, Eq, Debug)] |
| #[unstable(feature = "borrow_state", issue = "27733")] |
| pub enum BorrowState { |
| /// The cell is currently being read, there is at least one active `borrow`. |
| Reading, |
| /// The cell is currently being written to, there is an active `borrow_mut`. |
| Writing, |
| /// There are no outstanding borrows on this cell. |
| Unused, |
| } |
| |
| // Values [1, MAX-1] represent the number of `Ref` active |
| // (will not outgrow its range since `usize` is the size of the address space) |
| type BorrowFlag = usize; |
| const UNUSED: BorrowFlag = 0; |
| const WRITING: BorrowFlag = !0; |
| |
| impl<T> RefCell<T> { |
| /// Creates a new `RefCell` containing `value`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cell::RefCell; |
| /// |
| /// let c = RefCell::new(5); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub const fn new(value: T) -> RefCell<T> { |
| RefCell { |
| value: UnsafeCell::new(value), |
| borrow: Cell::new(UNUSED), |
| } |
| } |
| |
| /// Consumes the `RefCell`, returning the wrapped value. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cell::RefCell; |
| /// |
| /// let c = RefCell::new(5); |
| /// |
| /// let five = c.into_inner(); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn into_inner(self) -> T { |
| // Since this function takes `self` (the `RefCell`) by value, the |
| // compiler statically verifies that it is not currently borrowed. |
| // Therefore the following assertion is just a `debug_assert!`. |
| debug_assert!(self.borrow.get() == UNUSED); |
| unsafe { self.value.into_inner() } |
| } |
| } |
| |
| impl<T: ?Sized> RefCell<T> { |
| /// Query the current state of this `RefCell` |
| /// |
| /// The returned value can be dispatched on to determine if a call to |
| /// `borrow` or `borrow_mut` would succeed. |
| #[unstable(feature = "borrow_state", issue = "27733")] |
| #[inline] |
| pub fn borrow_state(&self) -> BorrowState { |
| match self.borrow.get() { |
| WRITING => BorrowState::Writing, |
| UNUSED => BorrowState::Unused, |
| _ => BorrowState::Reading, |
| } |
| } |
| |
| /// Immutably borrows the wrapped value. |
| /// |
| /// The borrow lasts until the returned `Ref` exits scope. Multiple |
| /// immutable borrows can be taken out at the same time. |
| /// |
| /// # Panics |
| /// |
| /// Panics if the value is currently mutably borrowed. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cell::RefCell; |
| /// |
| /// let c = RefCell::new(5); |
| /// |
| /// let borrowed_five = c.borrow(); |
| /// let borrowed_five2 = c.borrow(); |
| /// ``` |
| /// |
| /// An example of panic: |
| /// |
| /// ``` |
| /// use std::cell::RefCell; |
| /// use std::thread; |
| /// |
| /// let result = thread::spawn(move || { |
| /// let c = RefCell::new(5); |
| /// let m = c.borrow_mut(); |
| /// |
| /// let b = c.borrow(); // this causes a panic |
| /// }).join(); |
| /// |
| /// assert!(result.is_err()); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn borrow(&self) -> Ref<T> { |
| match BorrowRef::new(&self.borrow) { |
| Some(b) => Ref { |
| _value: unsafe { &*self.value.get() }, |
| _borrow: b, |
| }, |
| None => panic!("RefCell<T> already mutably borrowed"), |
| } |
| } |
| |
| /// Mutably borrows the wrapped value. |
| /// |
| /// The borrow lasts until the returned `RefMut` exits scope. The value |
| /// cannot be borrowed while this borrow is active. |
| /// |
| /// # Panics |
| /// |
| /// Panics if the value is currently borrowed. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cell::RefCell; |
| /// |
| /// let c = RefCell::new(5); |
| /// |
| /// let borrowed_five = c.borrow_mut(); |
| /// ``` |
| /// |
| /// An example of panic: |
| /// |
| /// ``` |
| /// use std::cell::RefCell; |
| /// use std::thread; |
| /// |
| /// let result = thread::spawn(move || { |
| /// let c = RefCell::new(5); |
| /// let m = c.borrow(); |
| /// |
| /// let b = c.borrow_mut(); // this causes a panic |
| /// }).join(); |
| /// |
| /// assert!(result.is_err()); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn borrow_mut(&self) -> RefMut<T> { |
| match BorrowRefMut::new(&self.borrow) { |
| Some(b) => RefMut { |
| _value: unsafe { &mut *self.value.get() }, |
| _borrow: b, |
| }, |
| None => panic!("RefCell<T> already borrowed"), |
| } |
| } |
| |
| /// Returns a reference to the underlying `UnsafeCell`. |
| /// |
| /// This can be used to circumvent `RefCell`'s safety checks. |
| /// |
| /// This function is `unsafe` because `UnsafeCell`'s field is public. |
| #[inline] |
| #[unstable(feature = "as_unsafe_cell", issue = "27708")] |
| pub unsafe fn as_unsafe_cell(&self) -> &UnsafeCell<T> { |
| &self.value |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| unsafe impl<T: ?Sized> Send for RefCell<T> where T: Send {} |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: Clone> Clone for RefCell<T> { |
| #[inline] |
| fn clone(&self) -> RefCell<T> { |
| RefCell::new(self.borrow().clone()) |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T:Default> Default for RefCell<T> { |
| #[inline] |
| fn default() -> RefCell<T> { |
| RefCell::new(Default::default()) |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: ?Sized + PartialEq> PartialEq for RefCell<T> { |
| #[inline] |
| fn eq(&self, other: &RefCell<T>) -> bool { |
| *self.borrow() == *other.borrow() |
| } |
| } |
| |
| #[stable(feature = "cell_eq", since = "1.2.0")] |
| impl<T: ?Sized + Eq> Eq for RefCell<T> {} |
| |
| struct BorrowRef<'b> { |
| _borrow: &'b Cell<BorrowFlag>, |
| } |
| |
| impl<'b> BorrowRef<'b> { |
| #[inline] |
| fn new(borrow: &'b Cell<BorrowFlag>) -> Option<BorrowRef<'b>> { |
| match borrow.get() { |
| WRITING => None, |
| b => { |
| borrow.set(b + 1); |
| Some(BorrowRef { _borrow: borrow }) |
| }, |
| } |
| } |
| } |
| |
| impl<'b> Drop for BorrowRef<'b> { |
| #[inline] |
| fn drop(&mut self) { |
| let borrow = self._borrow.get(); |
| debug_assert!(borrow != WRITING && borrow != UNUSED); |
| self._borrow.set(borrow - 1); |
| } |
| } |
| |
| impl<'b> Clone for BorrowRef<'b> { |
| #[inline] |
| fn clone(&self) -> BorrowRef<'b> { |
| // Since this Ref exists, we know the borrow flag |
| // is not set to WRITING. |
| let borrow = self._borrow.get(); |
| debug_assert!(borrow != WRITING && borrow != UNUSED); |
| self._borrow.set(borrow + 1); |
| BorrowRef { _borrow: self._borrow } |
| } |
| } |
| |
| /// Wraps a borrowed reference to a value in a `RefCell` box. |
| /// A wrapper type for an immutably borrowed value from a `RefCell<T>`. |
| /// |
| /// See the [module-level documentation](index.html) for more. |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub struct Ref<'b, T: ?Sized + 'b> { |
| // FIXME #12808: strange name to try to avoid interfering with |
| // field accesses of the contained type via Deref |
| _value: &'b T, |
| _borrow: BorrowRef<'b>, |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'b, T: ?Sized> Deref for Ref<'b, T> { |
| type Target = T; |
| |
| #[inline] |
| fn deref(&self) -> &T { |
| self._value |
| } |
| } |
| |
| impl<'b, T: ?Sized> Ref<'b, T> { |
| /// Copies a `Ref`. |
| /// |
| /// The `RefCell` is already immutably borrowed, so this cannot fail. |
| /// |
| /// This is an associated function that needs to be used as |
| /// `Ref::clone(...)`. A `Clone` implementation or a method would interfere |
| /// with the widespread use of `r.borrow().clone()` to clone the contents of |
| /// a `RefCell`. |
| #[unstable(feature = "cell_extras", |
| reason = "likely to be moved to a method, pending language changes", |
| issue = "27746")] |
| #[inline] |
| pub fn clone(orig: &Ref<'b, T>) -> Ref<'b, T> { |
| Ref { |
| _value: orig._value, |
| _borrow: orig._borrow.clone(), |
| } |
| } |
| |
| /// Make a new `Ref` for a component of the borrowed data. |
| /// |
| /// The `RefCell` is already immutably borrowed, so this cannot fail. |
| /// |
| /// This is an associated function that needs to be used as `Ref::map(...)`. |
| /// A method would interfere with methods of the same name on the contents |
| /// of a `RefCell` used through `Deref`. |
| /// |
| /// # Example |
| /// |
| /// ``` |
| /// #![feature(cell_extras)] |
| /// |
| /// use std::cell::{RefCell, Ref}; |
| /// |
| /// let c = RefCell::new((5, 'b')); |
| /// let b1: Ref<(u32, char)> = c.borrow(); |
| /// let b2: Ref<u32> = Ref::map(b1, |t| &t.0); |
| /// assert_eq!(*b2, 5) |
| /// ``` |
| #[unstable(feature = "cell_extras", reason = "recently added", |
| issue = "27746")] |
| #[inline] |
| pub fn map<U: ?Sized, F>(orig: Ref<'b, T>, f: F) -> Ref<'b, U> |
| where F: FnOnce(&T) -> &U |
| { |
| Ref { |
| _value: f(orig._value), |
| _borrow: orig._borrow, |
| } |
| } |
| |
| /// Make a new `Ref` for an optional component of the borrowed data, e.g. an |
| /// enum variant. |
| /// |
| /// The `RefCell` is already immutably borrowed, so this cannot fail. |
| /// |
| /// This is an associated function that needs to be used as |
| /// `Ref::filter_map(...)`. A method would interfere with methods of the |
| /// same name on the contents of a `RefCell` used through `Deref`. |
| /// |
| /// # Example |
| /// |
| /// ``` |
| /// # #![feature(cell_extras)] |
| /// use std::cell::{RefCell, Ref}; |
| /// |
| /// let c = RefCell::new(Ok(5)); |
| /// let b1: Ref<Result<u32, ()>> = c.borrow(); |
| /// let b2: Ref<u32> = Ref::filter_map(b1, |o| o.as_ref().ok()).unwrap(); |
| /// assert_eq!(*b2, 5) |
| /// ``` |
| #[unstable(feature = "cell_extras", reason = "recently added", |
| issue = "27746")] |
| #[inline] |
| pub fn filter_map<U: ?Sized, F>(orig: Ref<'b, T>, f: F) -> Option<Ref<'b, U>> |
| where F: FnOnce(&T) -> Option<&U> |
| { |
| f(orig._value).map(move |new| Ref { |
| _value: new, |
| _borrow: orig._borrow, |
| }) |
| } |
| } |
| |
| impl<'b, T: ?Sized> RefMut<'b, T> { |
| /// Make a new `RefMut` for a component of the borrowed data, e.g. an enum |
| /// variant. |
| /// |
| /// The `RefCell` is already mutably borrowed, so this cannot fail. |
| /// |
| /// This is an associated function that needs to be used as |
| /// `RefMut::map(...)`. A method would interfere with methods of the same |
| /// name on the contents of a `RefCell` used through `Deref`. |
| /// |
| /// # Example |
| /// |
| /// ``` |
| /// # #![feature(cell_extras)] |
| /// use std::cell::{RefCell, RefMut}; |
| /// |
| /// let c = RefCell::new((5, 'b')); |
| /// { |
| /// let b1: RefMut<(u32, char)> = c.borrow_mut(); |
| /// let mut b2: RefMut<u32> = RefMut::map(b1, |t| &mut t.0); |
| /// assert_eq!(*b2, 5); |
| /// *b2 = 42; |
| /// } |
| /// assert_eq!(*c.borrow(), (42, 'b')); |
| /// ``` |
| #[unstable(feature = "cell_extras", reason = "recently added", |
| issue = "27746")] |
| #[inline] |
| pub fn map<U: ?Sized, F>(orig: RefMut<'b, T>, f: F) -> RefMut<'b, U> |
| where F: FnOnce(&mut T) -> &mut U |
| { |
| RefMut { |
| _value: f(orig._value), |
| _borrow: orig._borrow, |
| } |
| } |
| |
| /// Make a new `RefMut` for an optional component of the borrowed data, e.g. |
| /// an enum variant. |
| /// |
| /// The `RefCell` is already mutably borrowed, so this cannot fail. |
| /// |
| /// This is an associated function that needs to be used as |
| /// `RefMut::filter_map(...)`. A method would interfere with methods of the |
| /// same name on the contents of a `RefCell` used through `Deref`. |
| /// |
| /// # Example |
| /// |
| /// ``` |
| /// # #![feature(cell_extras)] |
| /// use std::cell::{RefCell, RefMut}; |
| /// |
| /// let c = RefCell::new(Ok(5)); |
| /// { |
| /// let b1: RefMut<Result<u32, ()>> = c.borrow_mut(); |
| /// let mut b2: RefMut<u32> = RefMut::filter_map(b1, |o| { |
| /// o.as_mut().ok() |
| /// }).unwrap(); |
| /// assert_eq!(*b2, 5); |
| /// *b2 = 42; |
| /// } |
| /// assert_eq!(*c.borrow(), Ok(42)); |
| /// ``` |
| #[unstable(feature = "cell_extras", reason = "recently added", |
| issue = "27746")] |
| #[inline] |
| pub fn filter_map<U: ?Sized, F>(orig: RefMut<'b, T>, f: F) -> Option<RefMut<'b, U>> |
| where F: FnOnce(&mut T) -> Option<&mut U> |
| { |
| let RefMut { _value, _borrow } = orig; |
| f(_value).map(move |new| RefMut { |
| _value: new, |
| _borrow: _borrow, |
| }) |
| } |
| } |
| |
| struct BorrowRefMut<'b> { |
| _borrow: &'b Cell<BorrowFlag>, |
| } |
| |
| impl<'b> Drop for BorrowRefMut<'b> { |
| #[inline] |
| fn drop(&mut self) { |
| let borrow = self._borrow.get(); |
| debug_assert!(borrow == WRITING); |
| self._borrow.set(UNUSED); |
| } |
| } |
| |
| impl<'b> BorrowRefMut<'b> { |
| #[inline] |
| fn new(borrow: &'b Cell<BorrowFlag>) -> Option<BorrowRefMut<'b>> { |
| match borrow.get() { |
| UNUSED => { |
| borrow.set(WRITING); |
| Some(BorrowRefMut { _borrow: borrow }) |
| }, |
| _ => None, |
| } |
| } |
| } |
| |
| /// A wrapper type for a mutably borrowed value from a `RefCell<T>`. |
| /// |
| /// See the [module-level documentation](index.html) for more. |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub struct RefMut<'b, T: ?Sized + 'b> { |
| // FIXME #12808: strange name to try to avoid interfering with |
| // field accesses of the contained type via Deref |
| _value: &'b mut T, |
| _borrow: BorrowRefMut<'b>, |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'b, T: ?Sized> Deref for RefMut<'b, T> { |
| type Target = T; |
| |
| #[inline] |
| fn deref(&self) -> &T { |
| self._value |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'b, T: ?Sized> DerefMut for RefMut<'b, T> { |
| #[inline] |
| fn deref_mut(&mut self) -> &mut T { |
| self._value |
| } |
| } |
| |
| /// The core primitive for interior mutability in Rust. |
| /// |
| /// `UnsafeCell<T>` is a type that wraps some `T` and indicates unsafe interior operations on the |
| /// wrapped type. Types with an `UnsafeCell<T>` field are considered to have an 'unsafe interior'. |
| /// The `UnsafeCell<T>` type is the only legal way to obtain aliasable data that is considered |
| /// mutable. In general, transmuting an `&T` type into an `&mut T` is considered undefined behavior. |
| /// |
| /// Types like `Cell<T>` and `RefCell<T>` use this type to wrap their internal data. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cell::UnsafeCell; |
| /// use std::marker::Sync; |
| /// |
| /// # #[allow(dead_code)] |
| /// struct NotThreadSafe<T> { |
| /// value: UnsafeCell<T>, |
| /// } |
| /// |
| /// unsafe impl<T> Sync for NotThreadSafe<T> {} |
| /// ``` |
| #[lang = "unsafe_cell"] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub struct UnsafeCell<T: ?Sized> { |
| value: T, |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: ?Sized> !Sync for UnsafeCell<T> {} |
| |
| impl<T> UnsafeCell<T> { |
| /// Constructs a new instance of `UnsafeCell` which will wrap the specified |
| /// value. |
| /// |
| /// All access to the inner value through methods is `unsafe`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cell::UnsafeCell; |
| /// |
| /// let uc = UnsafeCell::new(5); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub const fn new(value: T) -> UnsafeCell<T> { |
| UnsafeCell { value: value } |
| } |
| |
| /// Unwraps the value. |
| /// |
| /// # Safety |
| /// |
| /// This function is unsafe because this thread or another thread may currently be |
| /// inspecting the inner value. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cell::UnsafeCell; |
| /// |
| /// let uc = UnsafeCell::new(5); |
| /// |
| /// let five = unsafe { uc.into_inner() }; |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub unsafe fn into_inner(self) -> T { |
| self.value |
| } |
| } |
| |
| impl<T: ?Sized> UnsafeCell<T> { |
| /// Gets a mutable pointer to the wrapped value. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cell::UnsafeCell; |
| /// |
| /// let uc = UnsafeCell::new(5); |
| /// |
| /// let five = uc.get(); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn get(&self) -> *mut T { |
| &self.value as *const T as *mut T |
| } |
| } |