Struct core::cell::RefCell 1.0.0[−][src]
pub struct RefCell<T: ?Sized> { /* fields omitted */ }Expand description
A mutable memory location with dynamically checked borrow rules
See the module-level documentation for more.
Implementations
Replaces the wrapped value with a new one, returning the old value, without deinitializing either one.
This function corresponds to std::mem::replace.
Panics
Panics if the value is currently borrowed.
Examples
use std::cell::RefCell;
let cell = RefCell::new(5);
let old_value = cell.replace(6);
assert_eq!(old_value, 5);
assert_eq!(cell, RefCell::new(6));Replaces the wrapped value with a new one computed from f, returning
the old value, without deinitializing either one.
Panics
Panics if the value is currently borrowed.
Examples
use std::cell::RefCell;
let cell = RefCell::new(5);
let old_value = cell.replace_with(|&mut old| old + 1);
assert_eq!(old_value, 5);
assert_eq!(cell, RefCell::new(6));Swaps the wrapped value of self with the wrapped value of other,
without deinitializing either one.
This function corresponds to std::mem::swap.
Panics
Panics if the value in either RefCell is currently borrowed.
Examples
use std::cell::RefCell;
let c = RefCell::new(5);
let d = RefCell::new(6);
c.swap(&d);
assert_eq!(c, RefCell::new(6));
assert_eq!(d, RefCell::new(5));Immutably borrows the wrapped value.
The borrow lasts until the returned Ref exits scope. Multiple
immutable borrows can be taken out at the same time.
Panics
Panics if the value is currently mutably borrowed. For a non-panicking variant, use
try_borrow.
Examples
use std::cell::RefCell;
let c = RefCell::new(5);
let borrowed_five = c.borrow();
let borrowed_five2 = c.borrow();An example of panic:
use std::cell::RefCell;
let c = RefCell::new(5);
let m = c.borrow_mut();
let b = c.borrow(); // this causes a panicImmutably borrows the wrapped value, returning an error if the value is currently mutably borrowed.
The borrow lasts until the returned Ref exits scope. Multiple immutable borrows can be
taken out at the same time.
This is the non-panicking variant of borrow.
Examples
use std::cell::RefCell;
let c = RefCell::new(5);
{
let m = c.borrow_mut();
assert!(c.try_borrow().is_err());
}
{
let m = c.borrow();
assert!(c.try_borrow().is_ok());
}Mutably borrows the wrapped value.
The borrow lasts until the returned RefMut or all RefMuts derived
from it exit scope. The value cannot be borrowed while this borrow is
active.
Panics
Panics if the value is currently borrowed. For a non-panicking variant, use
try_borrow_mut.
Examples
use std::cell::RefCell;
let c = RefCell::new("hello".to_owned());
*c.borrow_mut() = "bonjour".to_owned();
assert_eq!(&*c.borrow(), "bonjour");An example of panic:
use std::cell::RefCell;
let c = RefCell::new(5);
let m = c.borrow();
let b = c.borrow_mut(); // this causes a panicMutably borrows the wrapped value, returning an error if the value is currently borrowed.
The borrow lasts until the returned RefMut or all RefMuts derived
from it exit scope. The value cannot be borrowed while this borrow is
active.
This is the non-panicking variant of borrow_mut.
Examples
use std::cell::RefCell;
let c = RefCell::new(5);
{
let m = c.borrow();
assert!(c.try_borrow_mut().is_err());
}
assert!(c.try_borrow_mut().is_ok());Returns a mutable reference to the underlying data.
This call borrows RefCell mutably (at compile-time) so there is no
need for dynamic checks.
However be cautious: this method expects self to be mutable, which is
generally not the case when using a RefCell. Take a look at the
borrow_mut method instead if self isn’t mutable.
Also, please be aware that this method is only for special circumstances and is usually
not what you want. In case of doubt, use borrow_mut instead.
Examples
use std::cell::RefCell;
let mut c = RefCell::new(5);
*c.get_mut() += 1;
assert_eq!(c, RefCell::new(6));Undo the effect of leaked guards on the borrow state of the RefCell.
This call is similar to get_mut but more specialized. It borrows RefCell mutably to
ensure no borrows exist and then resets the state tracking shared borrows. This is relevant
if some Ref or RefMut borrows have been leaked.
Examples
#![feature(cell_leak)]
use std::cell::RefCell;
let mut c = RefCell::new(0);
std::mem::forget(c.borrow_mut());
assert!(c.try_borrow().is_err());
c.undo_leak();
assert!(c.try_borrow().is_ok());Immutably borrows the wrapped value, returning an error if the value is currently mutably borrowed.
Safety
Unlike RefCell::borrow, this method is unsafe because it does not
return a Ref, thus leaving the borrow flag untouched. Mutably
borrowing the RefCell while the reference returned by this method
is alive is undefined behaviour.
Examples
use std::cell::RefCell;
let c = RefCell::new(5);
{
let m = c.borrow_mut();
assert!(unsafe { c.try_borrow_unguarded() }.is_err());
}
{
let m = c.borrow();
assert!(unsafe { c.try_borrow_unguarded() }.is_ok());
}