Ref in std::cell - Rust (original) (raw)
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.
1.15.0 (const: unstable)
Copies a Ref.
The RefCell is already immutably borrowed, so this cannot fail.
This is an associated function that needs to be used asRef::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
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)1.63.0
Makes a new Ref for an optional component of the borrowed data. The original guard is returned as an Err(..) if the closure returnsNone.
The RefCell is already immutably borrowed, so this cannot fail.
This is an associated function that needs to be used asRef::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);🔬This is a nightly-only experimental API. (refcell_try_map #143801)
Tries to makes a new Ref 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 immutably borrowed, so this cannot fail.
This is an associated function that needs to be used asRef::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, Ref};
use std::str::{from_utf8, Utf8Error};
let c = RefCell::new(vec![0xF0, 0x9F, 0xA6 ,0x80]);
let b1: Ref<'_, Vec<u8>> = c.borrow();
let b2: Result<Ref<'_, str>, _> = Ref::try_map(b1, |v| from_utf8(v));
assert_eq!(&*b2.unwrap(), "🦀");
let c = RefCell::new(vec![0xF0, 0x9F, 0xA6]);
let b1: Ref<'_, Vec<u8>> = c.borrow();
let b2: Result<_, (Ref<'_, Vec<u8>>, Utf8Error)> = Ref::try_map(b1, |v| from_utf8(v));
let (b3, e) = b2.unwrap_err();
assert_eq!(*b3, vec![0xF0, 0x9F, 0xA6]);
assert_eq!(e.valid_up_to(), 0);1.35.0
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 asRef::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]);🔬This is a nightly-only experimental API. (cell_leak #69099)
Converts 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 asRef::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());1.0.0§
Formats the value using the given formatter. Read more
The resulting type after dereferencing.
Dereferences the value.
1.20.0§
Formats the value using the given formatter. Read more
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more
Returns the argument unchanged.
Calls U::from(self).
That is, this conversion is whatever the implementation of[From](../convert/trait.From.html "trait std::convert::From")<T> for U chooses to do.
🔬This is a nightly-only experimental API. (arbitrary_self_types #44874)
The target type on which the method may be called.
Converts the given value to a String. Read more
The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.