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-// Copyright 2012-2014 The Rust Project Developers.
-// See 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.
-
-//! A fork of std::cell::RefCell that makes `as_unsafe_cell` usable on stable Rust.
-//!
-//! FIXME(https://github.com/rust-lang/rust/issues/27708): Remove this
-//! (revert commit f7f81e0ed0b62402db291e28a9bb16f7194ebf78 / PR #11835)
-//! when `std::cell::RefCell::as_unsafe_cell` is in Rust’s stable channel.
-
-#![allow(unsafe_code, dead_code)]
-
-use std::cell::{UnsafeCell, Cell};
-use std::cmp::Ordering;
-use std::ops::{Deref, DerefMut};
-
-/// A fork of std::cell::RefCell that makes `as_unsafe_cell` usable on stable Rust.
-///
-/// FIXME(https://github.com/rust-lang/rust/issues/27708): Remove this
-/// (revert commit f7f81e0ed0b62402db291e28a9bb16f7194ebf78 / PR #11835)
-/// when `std::cell::RefCell::as_unsafe_cell` is in Rust’s stable channel.
-#[derive(Debug)]
-pub struct RefCell<T: ?Sized> {
- borrow: Cell<BorrowFlag>,
- value: UnsafeCell<T>,
-}
-type BorrowFlag = usize;
-
-/// An enumeration of values returned from the `state` method on a `RefCell<T>`.
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
-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)
-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);
- /// ```
- #[inline]
- pub 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();
- /// ```
- #[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.
- #[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());
- /// ```
- #[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);
- ///
- /// *c.borrow_mut() = 7;
- ///
- /// assert_eq!(*c.borrow(), 7);
- /// ```
- ///
- /// 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());
- /// ```
- #[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]
- pub unsafe fn as_unsafe_cell(&self) -> &UnsafeCell<T> {
- &self.value
- }
-
- /// Returns a mutable reference to the underlying data.
- ///
- /// This call borrows `RefCell` mutably (at compile-time) so there is no
- /// need for dynamic checks.
- #[inline]
- pub fn get_mut(&mut self) -> &mut T {
- unsafe {
- &mut *self.value.get()
- }
- }
-}
-
-unsafe impl<T: ?Sized> Send for RefCell<T> where T: Send {}
-
-impl<T: Clone> Clone for RefCell<T> {
- #[inline]
- fn clone(&self) -> RefCell<T> {
- RefCell::new(self.borrow().clone())
- }
-}
-
-impl<T: Default> Default for RefCell<T> {
- #[inline]
- fn default() -> RefCell<T> {
- RefCell::new(Default::default())
- }
-}
-
-impl<T: ?Sized + PartialEq> PartialEq for RefCell<T> {
- #[inline]
- fn eq(&self, other: &RefCell<T>) -> bool {
- *self.borrow() == *other.borrow()
- }
-}
-
-impl<T: ?Sized + Eq> Eq for RefCell<T> {}
-
-impl<T: ?Sized + PartialOrd> PartialOrd for RefCell<T> {
- #[inline]
- fn partial_cmp(&self, other: &RefCell<T>) -> Option<Ordering> {
- self.borrow().partial_cmp(&*other.borrow())
- }
-
- #[inline]
- fn lt(&self, other: &RefCell<T>) -> bool {
- *self.borrow() < *other.borrow()
- }
-
- #[inline]
- fn le(&self, other: &RefCell<T>) -> bool {
- *self.borrow() <= *other.borrow()
- }
-
- #[inline]
- fn gt(&self, other: &RefCell<T>) -> bool {
- *self.borrow() > *other.borrow()
- }
-
- #[inline]
- fn ge(&self, other: &RefCell<T>) -> bool {
- *self.borrow() >= *other.borrow()
- }
-}
-
-impl<T: ?Sized + Ord> Ord for RefCell<T> {
- #[inline]
- fn cmp(&self, other: &RefCell<T>) -> Ordering {
- self.borrow().cmp(&*other.borrow())
- }
-}
-
-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 != UNUSED);
- // Prevent the borrow counter from overflowing.
- assert!(borrow != WRITING);
- 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.
-pub struct Ref<'b, T: ?Sized + 'b> {
- value: &'b T,
- borrow: BorrowRef<'b>,
-}
-
-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`.
- #[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
- ///
- /// ```
- /// 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)
- /// ```
- #[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,
- }
- }
-}
-
-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
- ///
- /// ```
- /// 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'));
- /// ```
- #[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,
- }
- }
-}
-
-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.
-pub struct RefMut<'b, T: ?Sized + 'b> {
- value: &'b mut T,
- borrow: BorrowRefMut<'b>,
-}
-
-impl<'b, T: ?Sized> Deref for RefMut<'b, T> {
- type Target = T;
-
- #[inline]
- fn deref(&self) -> &T {
- self.value
- }
-}
-
-impl<'b, T: ?Sized> DerefMut for RefMut<'b, T> {
- #[inline]
- fn deref_mut(&mut self) -> &mut T {
- self.value
- }
-}
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