# Struct std::cell::RefMut

1.0.0 · source ·

    pub struct RefMut<'b, T>where
        T: 'b + ?Sized,{ /* private fields */ }

Expand description

A wrapper type for a mutably borrowed value from a `RefCell<T>`.

See the module-level documentation for more.

## Implementations§

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### impl<'b, T> RefMut<'b, T>where T: ?Sized,

1.8.0 · source

#### pub fn map<U, F>(orig: RefMut<'b, T>, f: F) -> RefMut<'b, U>where F: FnOnce(&mut T) -> &mut U, U: ?Sized,

Makes 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`.

##### Examples

    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'));

Run
1.63.0 · source

#### pub fn filter_map<U, F>( orig: RefMut<'b, T>, f: F ) -> Result<RefMut<'b, U>, RefMut<'b, T>>where F: FnOnce(&mut T) -> Option<&mut U>, U: ?Sized,

Makes a new `RefMut` for an optional component of the borrowed data. The original guard is returned as an `Err(..)` if the closure returns `None`.

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`.

##### Examples

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

    let c = RefCell::new(vec![1, 2, 3]);

    {
        let b1: RefMut<'_, Vec<u32>> = c.borrow_mut();
        let mut b2: Result<RefMut<'_, u32>, _> = RefMut::filter_map(b1, |v| v.get_mut(1));

        if let Ok(mut b2) = b2 {
            *b2 += 2;
        }
    }

    assert_eq!(*c.borrow(), vec![1, 4, 3]);

Run
1.35.0 · source

#### pub fn map_split<U, V, F>( orig: RefMut<'b, T>, f: F ) -> (RefMut<'b, U>, RefMut<'b, V>)where F: FnOnce(&mut T) -> (&mut U, &mut V), U: ?Sized, V: ?Sized,

Splits a `RefMut` into multiple `RefMut`s for different components of the borrowed data.

The underlying `RefCell` will remain mutably borrowed until both returned `RefMut`s go out of scope.

The `RefCell` is already mutably borrowed, so this cannot fail.

This is an associated function that needs to be used as `RefMut::map_split(...)`. A method would interfere with methods of the same name on the contents of a `RefCell` used through `Deref`.

##### Examples

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

    let cell = RefCell::new([1, 2, 3, 4]);
    let borrow = cell.borrow_mut();
    let (mut begin, mut end) = RefMut::map_split(borrow, |slice| slice.split_at_mut(2));
    assert_eq!(*begin, [1, 2]);
    assert_eq!(*end, [3, 4]);
    begin.copy_from_slice(&[4, 3]);
    end.copy_from_slice(&[2, 1]);

Run
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#### pub fn leak(orig: RefMut<'b, T>) -> &'b mut T

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

Convert into a mutable reference to the underlying data.

The underlying `RefCell` can not be borrowed from again and will always appear already mutably borrowed, making the returned reference the only to the interior.

This is an associated function that needs to be used as `RefMut::leak(...)`. A method would interfere with methods of the same name on the contents of a `RefCell` used through `Deref`.

##### Examples

    #![feature(cell_leak)]
    use std::cell::{RefCell, RefMut};
    let cell = RefCell::new(0);

    let value = RefMut::leak(cell.borrow_mut());
    assert_eq!(*value, 0);
    *value = 1;

    assert!(cell.try_borrow_mut().is_err());

Run

## Trait Implementations§

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### impl<T> Debug for RefMut<'_, T>where T: Debug + ?Sized,

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

Formats the value using the given formatter. Read more
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### impl<T> Deref for RefMut<'_, T>where T: ?Sized,

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#### type Target = T

The resulting type after dereferencing.
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#### fn deref(&self) -> &T

Dereferences the value.
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### impl<T> DerefMut for RefMut<'_, T>where T: ?Sized,

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#### fn deref_mut(&mut self) -> &mut T

Mutably dereferences the value.
1.20.0 · source§

### impl<T> Display for RefMut<'_, T>where T: Display + ?Sized,

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

Formats the value using the given formatter. Read more
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### impl<'b, T, U> CoerceUnsized<RefMut<'b, U>> for RefMut<'b, T>where T: Unsize<U> + ?Sized, U: ?Sized,

## Auto Trait Implementations§

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### impl<'b, T> !RefUnwindSafe for RefMut<'b, T>

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### impl<'b, T> !Send for RefMut<'b, T>

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### impl<'b, T> !Sync for RefMut<'b, T>

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### impl<'b, T: ?Sized> Unpin for RefMut<'b, T>

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### impl<'b, T> !UnwindSafe for RefMut<'b, T>

## Blanket Implementations§

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### impl<T> Any for Twhere T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for Twhere T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for Twhere T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for Twhere U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T> ToString for Twhere T: Display + ?Sized,

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#### default fn to_string(&self) -> String

Converts the given value to a `String`. Read more
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### impl<T, U> TryFrom<U> for Twhere U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.