Struct std::cell::RefCell

pub struct RefCell<T> where
    T: ?Sized, { /* private fields */ }

A mutable memory location with dynamically checked borrow rules

See the module-level documentation for more.

Implementations

impl<T> RefCell<T>

pub const fn new(value: T) -> RefCell<T>

Creates a new RefCell containing value.

Examples

use std::cell::RefCell;

let c = RefCell::new(5);

pub fn into_inner(self) -> T

Consumes the RefCell, returning the wrapped value.

Examples

use std::cell::RefCell;

let c = RefCell::new(5);

let five = c.into_inner();

pub fn replace(&self, t: T) -> T

Replaces the wrapped value with a new one, returning the old value, without deinitializing either one.

This function corresponds to std::mem::replace.

Panics

Panics if the value is currently borrowed.

Examples

use std::cell::RefCell;
let cell = RefCell::new(5);
let old_value = cell.replace(6);
assert_eq!(old_value, 5);
assert_eq!(cell, RefCell::new(6));

pub fn replace_with<F>(&self, f: F) -> T where
    F: FnOnce(&mut T) -> T, 

Replaces the wrapped value with a new one computed from f, returning the old value, without deinitializing either one.

Panics

Panics if the value is currently borrowed.

Examples

use std::cell::RefCell;
let cell = RefCell::new(5);
let old_value = cell.replace_with(|&mut old| old + 1);
assert_eq!(old_value, 5);
assert_eq!(cell, RefCell::new(6));

pub fn swap(&self, other: &RefCell<T>)

Swaps the wrapped value of self with the wrapped value of other, without deinitializing either one.

This function corresponds to std::mem::swap.

Panics

Panics if the value in either RefCell is currently borrowed.

Examples

use std::cell::RefCell;
let c = RefCell::new(5);
let d = RefCell::new(6);
c.swap(&d);
assert_eq!(c, RefCell::new(6));
assert_eq!(d, RefCell::new(5));

impl<T> RefCell<T> where
    T: ?Sized, 

pub fn borrow(&self) -> Ref<'_, T>

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. For a non-panicking variant, use try_borrow.

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;

let c = RefCell::new(5);

let m = c.borrow_mut();
let b = c.borrow(); // this causes a panic

pub fn try_borrow(&self) -> Result<Ref<'_, T>, BorrowError>

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.

Examples

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());
}

pub fn borrow_mut(&self) -> RefMut<'_, T>

Mutably borrows the wrapped value.

The borrow lasts until the returned RefMut or all RefMuts derived from it exit scope. The value cannot be borrowed while this borrow is active.

Panics

Panics if the value is currently borrowed. For a non-panicking variant, use try_borrow_mut.

Examples

use std::cell::RefCell;

let c = RefCell::new("hello".to_owned());

*c.borrow_mut() = "bonjour".to_owned();

assert_eq!(&*c.borrow(), "bonjour");

An example of panic:

use std::cell::RefCell;

let c = RefCell::new(5);
let m = c.borrow();

let b = c.borrow_mut(); // this causes a panic

pub fn try_borrow_mut(&self) -> Result<RefMut<'_, T>, BorrowMutError>

Mutably borrows the wrapped value, returning an error if the value is currently borrowed.

The borrow lasts until the returned RefMut or all RefMuts derived from it exit scope. The value cannot be borrowed while this borrow is active.

This is the non-panicking variant of borrow_mut.

Examples

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());

pub fn as_ptr(&self) -> *mut T

Returns a raw pointer to the underlying data in this cell.

Examples

use std::cell::RefCell;

let c = RefCell::new(5);

let ptr = c.as_ptr();

pub fn get_mut(&mut self) -> &mut T

Returns a mutable reference to the underlying data.

This call borrows RefCell mutably (at compile-time) so there is no need for dynamic checks.

However be cautious: this method expects self to be mutable, which is generally not the case when using a RefCell. Take a look at the borrow_mut method instead if self isn’t mutable.

Also, please be aware that this method is only for special circumstances and is usually not what you want. In case of doubt, use borrow_mut instead.

Examples

use std::cell::RefCell;

let mut c = RefCell::new(5);
*c.get_mut() += 1;

assert_eq!(c, RefCell::new(6));

pub fn undo_leak(&mut self) -> &mut T

🔬This is a nightly-only experimental API. (cell_leak #69099)

Undo the effect of leaked guards on the borrow state of the RefCell.

This call is similar to get_mut but more specialized. It borrows RefCell mutably to ensure no borrows exist and then resets the state tracking shared borrows. This is relevant if some Ref or RefMut borrows have been leaked.

Examples

#![feature(cell_leak)]
use std::cell::RefCell;

let mut c = RefCell::new(0);
std::mem::forget(c.borrow_mut());

assert!(c.try_borrow().is_err());
c.undo_leak();
assert!(c.try_borrow().is_ok());

pub unsafe fn try_borrow_unguarded(&self) -> Result<&T, BorrowError>

Immutably borrows the wrapped value, returning an error if the value is currently mutably borrowed.

Safety

Unlike RefCell::borrow, this method is unsafe because it does not return a Ref, thus leaving the borrow flag untouched. Mutably borrowing the RefCell while the reference returned by this method is alive is undefined behaviour.

Examples

use std::cell::RefCell;

let c = RefCell::new(5);

{
    let m = c.borrow_mut();
    assert!(unsafe { c.try_borrow_unguarded() }.is_err());
}

{
    let m = c.borrow();
    assert!(unsafe { c.try_borrow_unguarded() }.is_ok());
}

impl<T> RefCell<T> where
    T: Default, 

pub fn take(&self) -> T

Takes the wrapped value, leaving Default::default() in its place.

Panics

Panics if the value is currently borrowed.

Examples

use std::cell::RefCell;

let c = RefCell::new(5);
let five = c.take();

assert_eq!(five, 5);
assert_eq!(c.into_inner(), 0);

Trait Implementations

impl<T> Clone for RefCell<T> where
    T: Clone, 

fn clone(&self) -> RefCell<T>

Panics

Panics if the value is currently mutably borrowed.

fn clone_from(&mut self, other: &RefCell<T>)

Panics

Panics if other is currently mutably borrowed.

impl<T> Debug for RefCell<T> where
    T: Debug + ?Sized, 

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<T> Default for RefCell<T> where
    T: Default, 

fn default() -> RefCell<T>

Creates a RefCell<T>, with the Default value for T.

impl<T> From<T> for RefCell<T>

fn from(t: T) -> RefCell<T>

Creates a new RefCell<T> containing the given value.

impl<T> Ord for RefCell<T> where
    T: Ord + ?Sized, 

fn cmp(&self, other: &RefCell<T>) -> Ordering

Panics

Panics if the value in either RefCell is currently borrowed.

impl<T> PartialEq<RefCell<T>> for RefCell<T> where
    T: PartialEq<T> + ?Sized, 

fn eq(&self, other: &RefCell<T>) -> bool

Panics

Panics if the value in either RefCell is currently borrowed.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T> PartialOrd<RefCell<T>> for RefCell<T> where
    T: PartialOrd<T> + ?Sized, 

fn partial_cmp(&self, other: &RefCell<T>) -> Option<Ordering>

Panics

Panics if the value in either RefCell is currently borrowed.

fn lt(&self, other: &RefCell<T>) -> bool

Panics

Panics if the value in either RefCell is currently borrowed.

fn le(&self, other: &RefCell<T>) -> bool

Panics

Panics if the value in either RefCell is currently borrowed.

fn gt(&self, other: &RefCell<T>) -> bool

Panics

Panics if the value in either RefCell is currently borrowed.

fn ge(&self, other: &RefCell<T>) -> bool

Panics

Panics if the value in either RefCell is currently borrowed.

impl<T, U> CoerceUnsized<RefCell<U>> for RefCell<T> where
    T: CoerceUnsized<U>, 

impl<T> Eq for RefCell<T> where
    T: Eq + ?Sized, 

impl<T> Send for RefCell<T> where
    T: Send + ?Sized, 

impl<T> !Sync for RefCell<T> where
    T: ?Sized,