# Struct 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'));

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]);

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

🔬This is a nightly-only experimental API. (`refcell_try_map` #143801)

Tries to makes a new `RefMut` for a component of the borrowed data. On failure, the original guard is returned alongside with the error returned by the closure.

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

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

##### §Examples

    #![feature(refcell_try_map)]
    use std::cell::{RefCell, RefMut};
    use std::str::{from_utf8_mut, Utf8Error};

    let c = RefCell::new(vec![0x68, 0x65, 0x6C, 0x6C, 0x6F]);
    {
        let b1: RefMut<'_, Vec<u8>> = c.borrow_mut();
        let b2: Result<RefMut<'_, str>, _> = RefMut::try_map(b1, |v| from_utf8_mut(v));
        let mut b2 = b2.unwrap();
        assert_eq!(&*b2, "hello");
        b2.make_ascii_uppercase();
    }
    assert_eq!(*c.borrow(), "HELLO".as_bytes());

    let c = RefCell::new(vec![0xFF]);
    let b1: RefMut<'_, Vec<u8>> = c.borrow_mut();
    let b2: Result<_, (RefMut<'_, Vec<u8>>, Utf8Error)> = RefMut::try_map(b1, |v| from_utf8_mut(v));
    let (b3, e) = b2.unwrap_err();
    assert_eq!(*b3, vec![0xFF]);
    assert_eq!(e.valid_up_to(), 0);

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]);

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

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

Converts 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());

## Trait Implementations§

1.0.0 · Source§

### 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
1.0.0 (const: unstable) · Source§

### 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.
1.0.0 (const: unstable) · Source§

### 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,

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

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

## Auto Trait Implementations§

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

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

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

## Blanket Implementations§

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### impl<T> Any for T
where 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 T
where 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 T
where 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 T
where 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<P, T> Receiver for P
where P: Deref<Target = T> + ?Sized, T: ?Sized,

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#### type Target = T

🔬This is a nightly-only experimental API. (`arbitrary_self_types` #44874)
The target type on which the method may be called.
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### impl<T> ToString for T
where T: Display + ?Sized,

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

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