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Auto merge of rust-lang#35425 - apasel422:refcell, r=alexcrichton
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Implement `RefCell::{try_borrow, try_borrow_mut}`

CC rust-lang#35070

r? @alexcrichton
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bors authored Aug 9, 2016
2 parents 58c5716 + a20a1db commit c2b03f8
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Showing 3 changed files with 132 additions and 9 deletions.
125 changes: 116 additions & 9 deletions src/libcore/cell.rs
Original file line number Diff line number Diff line change
Expand Up @@ -147,10 +147,13 @@
use clone::Clone;
use cmp::{PartialEq, Eq, PartialOrd, Ord, Ordering};
use default::Default;
use marker::{Copy, Send, Sync, Sized, Unsize};
use fmt::{self, Debug, Display};
use marker::{Copy, PhantomData, Send, Sync, Sized, Unsize};
use ops::{Deref, DerefMut, Drop, FnOnce, CoerceUnsized};
use option::Option;
use option::Option::{None, Some};
use result::Result;
use result::Result::{Ok, Err};

/// A mutable memory location that admits only `Copy` data.
///
Expand Down Expand Up @@ -347,6 +350,46 @@ pub enum BorrowState {
Unused,
}

/// An error returned by [`RefCell::try_borrow`](struct.RefCell.html#method.try_borrow).
#[unstable(feature = "try_borrow", issue = "35070")]
pub struct BorrowError<'a, T: 'a + ?Sized> {
marker: PhantomData<&'a RefCell<T>>,
}

#[unstable(feature = "try_borrow", issue = "35070")]
impl<'a, T: ?Sized> Debug for BorrowError<'a, T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("BorrowError").finish()
}
}

#[unstable(feature = "try_borrow", issue = "35070")]
impl<'a, T: ?Sized> Display for BorrowError<'a, T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
Display::fmt("already mutably borrowed", f)
}
}

/// An error returned by [`RefCell::try_borrow_mut`](struct.RefCell.html#method.try_borrow_mut).
#[unstable(feature = "try_borrow", issue = "35070")]
pub struct BorrowMutError<'a, T: 'a + ?Sized> {
marker: PhantomData<&'a RefCell<T>>,
}

#[unstable(feature = "try_borrow", issue = "35070")]
impl<'a, T: ?Sized> Debug for BorrowMutError<'a, T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("BorrowMutError").finish()
}
}

#[unstable(feature = "try_borrow", issue = "35070")]
impl<'a, T: ?Sized> Display for BorrowMutError<'a, T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
Display::fmt("already borrowed", f)
}
}

// 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;
Expand Down Expand Up @@ -432,7 +475,8 @@ impl<T: ?Sized> RefCell<T> {
///
/// # Panics
///
/// Panics if the value is currently mutably borrowed.
/// Panics if the value is currently mutably borrowed. For a non-panicking variant, use
/// [`try_borrow`](#method.try_borrow).
///
/// # Examples
///
Expand Down Expand Up @@ -463,12 +507,45 @@ impl<T: ?Sized> RefCell<T> {
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn borrow(&self) -> Ref<T> {
self.try_borrow().expect("already mutably borrowed")
}

/// Immutably borrows the wrapped value, returning an error if the value is currently mutably
/// borrowed.
///
/// The borrow lasts until the returned `Ref` exits scope. Multiple immutable borrows can be
/// taken out at the same time.
///
/// This is the non-panicking variant of [`borrow`](#method.borrow).
///
/// # Examples
///
/// ```
/// #![feature(try_borrow)]
///
/// use std::cell::RefCell;
///
/// let c = RefCell::new(5);
///
/// {
/// let m = c.borrow_mut();
/// assert!(c.try_borrow().is_err());
/// }
///
/// {
/// let m = c.borrow();
/// assert!(c.try_borrow().is_ok());
/// }
/// ```
#[unstable(feature = "try_borrow", issue = "35070")]
#[inline]
pub fn try_borrow(&self) -> Result<Ref<T>, BorrowError<T>> {
match BorrowRef::new(&self.borrow) {
Some(b) => Ref {
Some(b) => Ok(Ref {
value: unsafe { &*self.value.get() },
borrow: b,
},
None => panic!("RefCell<T> already mutably borrowed"),
}),
None => Err(BorrowError { marker: PhantomData }),
}
}

Expand All @@ -479,7 +556,8 @@ impl<T: ?Sized> RefCell<T> {
///
/// # Panics
///
/// Panics if the value is currently borrowed.
/// Panics if the value is currently borrowed. For a non-panicking variant, use
/// [`try_borrow_mut`](#method.try_borrow_mut).
///
/// # Examples
///
Expand Down Expand Up @@ -511,12 +589,41 @@ impl<T: ?Sized> RefCell<T> {
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn borrow_mut(&self) -> RefMut<T> {
self.try_borrow_mut().expect("already borrowed")
}

/// Mutably borrows the wrapped value, returning an error if the value is currently borrowed.
///
/// The borrow lasts until the returned `RefMut` exits scope. The value cannot be borrowed
/// while this borrow is active.
///
/// This is the non-panicking variant of [`borrow_mut`](#method.borrow_mut).
///
/// # Examples
///
/// ```
/// #![feature(try_borrow)]
///
/// use std::cell::RefCell;
///
/// let c = RefCell::new(5);
///
/// {
/// let m = c.borrow();
/// assert!(c.try_borrow_mut().is_err());
/// }
///
/// assert!(c.try_borrow_mut().is_ok());
/// ```
#[unstable(feature = "try_borrow", issue = "35070")]
#[inline]
pub fn try_borrow_mut(&self) -> Result<RefMut<T>, BorrowMutError<T>> {
match BorrowRefMut::new(&self.borrow) {
Some(b) => RefMut {
Some(b) => Ok(RefMut {
value: unsafe { &mut *self.value.get() },
borrow: b,
},
None => panic!("RefCell<T> already borrowed"),
}),
None => Err(BorrowMutError { marker: PhantomData }),
}
}

Expand Down
15 changes: 15 additions & 0 deletions src/libstd/error.rs
Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,7 @@

use any::TypeId;
use boxed::Box;
use cell;
use char;
use fmt::{self, Debug, Display};
use marker::{Send, Sync, Reflect};
Expand Down Expand Up @@ -289,6 +290,20 @@ impl Error for fmt::Error {
}
}

#[unstable(feature = "try_borrow", issue = "35070")]
impl<'a, T: ?Sized + Reflect> Error for cell::BorrowError<'a, T> {
fn description(&self) -> &str {
"already mutably borrowed"
}
}

#[unstable(feature = "try_borrow", issue = "35070")]
impl<'a, T: ?Sized + Reflect> Error for cell::BorrowMutError<'a, T> {
fn description(&self) -> &str {
"already borrowed"
}
}

// copied from any.rs
impl Error + 'static {
/// Returns true if the boxed type is the same as `T`
Expand Down
1 change: 1 addition & 0 deletions src/libstd/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -269,6 +269,7 @@
#![feature(str_utf16)]
#![feature(test, rustc_private)]
#![feature(thread_local)]
#![feature(try_borrow)]
#![feature(try_from)]
#![feature(unboxed_closures)]
#![feature(unicode)]
Expand Down

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