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; }
The IndexMut trait is used to specify the functionality of indexing
operations like container[index] when used in a mutable context.
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 if value implements Copy.
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, } } } fn main() { 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
The method for the mutable indexing (container[index]) operation
Implementors
impl IndexMut<RangeFull> for strimpl IndexMut<RangeInclusive<usize>> for strimpl IndexMut<RangeToInclusive<usize>> for strimpl<T, I> IndexMut<I> for [T] where
I: SliceIndex<[T]>,impl IndexMut<RangeTo<usize>> for strimpl IndexMut<RangeFrom<usize>> for strimpl IndexMut<Range<usize>> for strimpl<T> IndexMut<Range<usize>> for Vec<T>impl IndexMut<RangeInclusive<usize>> for Stringimpl<T> IndexMut<RangeFrom<usize>> for Vec<T>impl IndexMut<Range<usize>> for Stringimpl<T> IndexMut<RangeToInclusive<usize>> for Vec<T>impl IndexMut<RangeTo<usize>> for Stringimpl<T> IndexMut<usize> for Vec<T>impl IndexMut<RangeFull> for Stringimpl<T> IndexMut<RangeInclusive<usize>> for Vec<T>impl<T> IndexMut<RangeFull> for Vec<T>impl<T> IndexMut<RangeTo<usize>> for Vec<T>impl<A> IndexMut<usize> for VecDeque<A>impl IndexMut<RangeFrom<usize>> for Stringimpl IndexMut<RangeToInclusive<usize>> for String