Trait std::ops::IndexMut 1.0.0
[−]
[src]
#[lang = "index_mut"]pub trait IndexMut<Idx>: Index<Idx> where
Idx: ?Sized, { fn index_mut(&mut self, index: Idx) -> &mut Self::Output; }
Used for indexing operations (container[index]
) in mutable contexts.
container[index]
is actually syntactic sugar for
*container.index_mut(index)
, but only when used as a mutable value. If
an immutable value is requested, the Index
trait is used instead. This
allows nice things such as v[index] = value
.
Examples
A very simple implementation of a Balance
struct that has two sides, where
each can be indexed mutably and immutably.
use std::ops::{Index,IndexMut}; #[derive(Debug)] enum Side { Left, Right, } #[derive(Debug, PartialEq)] enum Weight { Kilogram(f32), Pound(f32), } struct Balance { pub left: Weight, pub right: Weight, } impl Index<Side> for Balance { type Output = Weight; fn index<'a>(&'a self, index: Side) -> &'a Weight { println!("Accessing {:?}-side of balance immutably", index); match index { Side::Left => &self.left, Side::Right => &self.right, } } } impl IndexMut<Side> for Balance { fn index_mut<'a>(&'a mut self, index: Side) -> &'a mut Weight { println!("Accessing {:?}-side of balance mutably", index); match index { Side::Left => &mut self.left, Side::Right => &mut self.right, } } } let mut balance = Balance { right: Weight::Kilogram(2.5), left: Weight::Pound(1.5), }; // In this case, `balance[Side::Right]` is sugar for // `*balance.index(Side::Right)`, since we are only *reading* // `balance[Side::Right]`, not writing it. assert_eq!(balance[Side::Right], Weight::Kilogram(2.5)); // However, in this case `balance[Side::Left]` is sugar for // `*balance.index_mut(Side::Left)`, since we are writing // `balance[Side::Left]`. balance[Side::Left] = Weight::Kilogram(3.0);Run
Required Methods
fn index_mut(&mut self, index: Idx) -> &mut Self::Output
Performs the mutable indexing (container[index]
) operation.
Implementors
impl IndexMut<RangeFull> for str
impl IndexMut<RangeInclusive<usize>> for str
impl IndexMut<RangeToInclusive<usize>> for str
impl IndexMut<RangeTo<usize>> for str
impl<T, I> IndexMut<I> for [T] where
I: SliceIndex<[T]>,impl IndexMut<RangeFrom<usize>> for str
impl IndexMut<Range<usize>> for str
impl IndexMut<RangeTo<usize>> for String
impl<A> IndexMut<usize> for VecDeque<A>
impl<T> IndexMut<Range<usize>> for Vec<T>
impl IndexMut<RangeInclusive<usize>> for String
impl IndexMut<RangeToInclusive<usize>> for String
impl<T> IndexMut<RangeFull> for Vec<T>
impl<T> IndexMut<RangeTo<usize>> for Vec<T>
impl IndexMut<Range<usize>> for String
impl<T> IndexMut<RangeToInclusive<usize>> for Vec<T>
impl<T> IndexMut<RangeInclusive<usize>> for Vec<T>
impl IndexMut<RangeFrom<usize>> for String
impl<T> IndexMut<usize> for Vec<T>
impl<T> IndexMut<RangeFrom<usize>> for Vec<T>
impl IndexMut<RangeFull> for String