# Struct std::cell::RefCell 1.0.0 [−] [src]

    pub struct RefCell<T> where T: ?Sized {
        // some fields omitted
    }

A mutable memory location with dynamically checked borrow rules

See the module-level documentation for more.

## Methods

### `impl<T> RefCell<T>`

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

Creates a new `RefCell` containing `value`.

# Examples

fn main() { use std::cell::RefCell; let c = RefCell::new(5); }

    use std::cell::RefCell;

    let c = RefCell::new(5);

#### `fn into_inner(self) -> T`

Consumes the `RefCell`, returning the wrapped value.

# Examples

fn main() { use std::cell::RefCell; let c = RefCell::new(5); let five = c.into_inner(); }

    use std::cell::RefCell;

    let c = RefCell::new(5);

    let five = c.into_inner();

### `impl<T> RefCell<T> where T: ?Sized`

#### `fn borrow_state(&self) -> BorrowState`

Unstable (`borrow_state` #27733)

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.

# Examples

#![feature(borrow_state)] fn main() { use std::cell::{BorrowState, RefCell}; let c = RefCell::new(5); match c.borrow_state() { BorrowState::Writing => println!("Cannot be borrowed"), BorrowState::Reading => println!("Cannot be borrowed mutably"), BorrowState::Unused => println!("Can be borrowed (mutably as well)"), } }

    #![feature(borrow_state)]

    use std::cell::{BorrowState, RefCell};

    let c = RefCell::new(5);

    match c.borrow_state() {
        BorrowState::Writing => println!("Cannot be borrowed"),
        BorrowState::Reading => println!("Cannot be borrowed mutably"),
        BorrowState::Unused => println!("Can be borrowed (mutably as well)"),
    }

#### `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.

# Examples

fn main() { use std::cell::RefCell; let c = RefCell::new(5); let borrowed_five = c.borrow(); let borrowed_five2 = c.borrow(); }

    use std::cell::RefCell;

    let c = RefCell::new(5);

    let borrowed_five = c.borrow();
    let borrowed_five2 = c.borrow();

An example of panic:

fn main() { 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()); }

    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());

#### `fn borrow_mut(&self) -> RefMut<T>`

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

fn main() { use std::cell::RefCell; let c = RefCell::new(5); *c.borrow_mut() = 7; assert_eq!(*c.borrow(), 7); }

    use std::cell::RefCell;

    let c = RefCell::new(5);

    *c.borrow_mut() = 7;

    assert_eq!(*c.borrow(), 7);

An example of panic:

fn main() { 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()); }

    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());

#### `unsafe fn as_unsafe_cell(&self) -> &UnsafeCell<T>`

Unstable (`as_unsafe_cell` #27708)

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.

# Examples

#![feature(as_unsafe_cell)] fn main() { use std::cell::RefCell; let c = RefCell::new(5); let c = unsafe { c.as_unsafe_cell() }; }

    #![feature(as_unsafe_cell)]

    use std::cell::RefCell;

    let c = RefCell::new(5);
    let c = unsafe { c.as_unsafe_cell() };

#### `fn get_mut(&mut self) -> &mut T`
1.11.0

Returns a mutable reference to the underlying data.

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

# Examples

fn main() { use std::cell::RefCell; let mut c = RefCell::new(5); *c.get_mut() += 1; assert_eq!(c, RefCell::new(6)); }

    use std::cell::RefCell;

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

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

## Trait Implementations

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

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

### `impl<T> Clone for RefCell<T> where T: Clone`

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

Returns a copy of the value. Read more

#### `fn clone_from(&mut self, source: &Self)`

Performs copy-assignment from `source`. Read more

### `impl<T> Default for RefCell<T> where T: Default`

#### `fn default() -> RefCell<T>`

Returns the "default value" for a type. Read more

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

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

This method tests for `self` and `other` values to be equal, and is used by `==`. Read more

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

This method tests for `!=`.

### `impl<T> Eq for RefCell<T> where T: Eq + ?Sized`
1.2.0

### `impl<T> PartialOrd<RefCell<T>> for RefCell<T> where T: PartialOrd<T> + ?Sized`
1.10.0

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

This method returns an ordering between `self` and `other` values if one exists. Read more

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

This method tests less than (for `self` and `other`) and is used by the `<` operator. Read more

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

This method tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more

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

This method tests greater than (for `self` and `other`) and is used by the `>` operator. Read more

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

This method tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more

### `impl<T> Ord for RefCell<T> where T: Ord + ?Sized`
1.10.0

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

This method returns an `Ordering` between `self` and `other`. Read more

### `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.

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