Struct core::cell::Ref

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

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

impl<'b, T: ?Sized> Ref<'b, T>

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.

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

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)

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

🔬 This is a nightly-only experimental API. (cell_filter_map #81061)

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

#![feature(cell_filter_map)]

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);

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

Splits a Ref into multiple Refs 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]);

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());

Trait Implementations

impl<T: ?Sized + Debug> Debug for Ref<'_, T>

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

Formats the value using the given formatter.

impl<T: ?Sized> Deref for Ref<'_, T>

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &T

Dereferences the value.

impl<T: ?Sized + Display> Display for Ref<'_, T>

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

Formats the value using the given formatter.

impl<'b, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Ref<'b, U>> for Ref<'b, T>