# Struct std::cell::Ref

1.0.0 · source ·

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

Expand description

Wraps a borrowed reference to a value in a `RefCell` box. A wrapper type for an immutably borrowed value from a `RefCell<T>`.

See the module-level documentation for more.

## Implementations§

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

1.15.0 · source

#### pub fn clone(orig: &Ref<'b, T>) -> Ref<'b, T>

Copies a `Ref`.

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

This is an associated function that needs to be used as `Ref::clone(...)`. A `Clone` implementation or a method would interfere with the widespread use of `r.borrow().clone()` to clone the contents of a `RefCell`.

1.8.0 · source

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

Makes a new `Ref` for a component of the borrowed data.

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

This is an associated function that needs to be used as `Ref::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, Ref};

    let c = RefCell::new((5, 'b'));
    let b1: Ref<'_, (u32, char)> = c.borrow();
    let b2: Ref<'_, u32> = Ref::map(b1, |t| &t.0);
    assert_eq!(*b2, 5)

Run
1.63.0 · source

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

Makes a new `Ref` 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 immutably borrowed, so this cannot fail.

This is an associated function that needs to be used as `Ref::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, Ref};

    let c = RefCell::new(vec![1, 2, 3]);
    let b1: Ref<'_, Vec<u32>> = c.borrow();
    let b2: Result<Ref<'_, u32>, _> = Ref::filter_map(b1, |v| v.get(1));
    assert_eq!(*b2.unwrap(), 2);

Run
1.35.0 · source

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

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

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

This is an associated function that needs to be used as `Ref::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::{Ref, RefCell};

    let cell = RefCell::new([1, 2, 3, 4]);
    let borrow = cell.borrow();
    let (begin, end) = Ref::map_split(borrow, |slice| slice.split_at(2));
    assert_eq!(*begin, [1, 2]);
    assert_eq!(*end, [3, 4]);

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

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

Convert into a reference to the underlying data.

The underlying `RefCell` can never be mutably borrowed from again and will always appear already immutably borrowed. It is not a good idea to leak more than a constant number of references. The `RefCell` can be immutably borrowed again if only a smaller number of leaks have occurred in total.

This is an associated function that needs to be used as `Ref::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, Ref};
    let cell = RefCell::new(0);

    let value = Ref::leak(cell.borrow());
    assert_eq!(*value, 0);

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

Run

## Trait Implementations§

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### impl<T> Debug for Ref<'_, 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 Ref<'_, 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.
1.20.0 · source§

### impl<T> Display for Ref<'_, 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<Ref<'b, U>> for Ref<'b, T>where T: Unsize<U> + ?Sized, U: ?Sized,

## Auto Trait Implementations§

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

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

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

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

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### impl<'b, T> !UnwindSafe for Ref<'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.