Trait nom::lib::std::ops::IndexMut

#[lang = "index_mut"]
pub trait IndexMut<Idx>: Index<Idx> where
    Idx: ?Sized, {
    pub fn index_mut(&mut self, index: Idx) -> &mut Self::Output;
}

[−] Expand description

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(&self, index: Side) -> &Self::Output {
        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(&mut self, index: Side) -> &mut Self::Output {
        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);

Required methods

pub fn index_mut(&mut self, index: Idx) -> &mut Self::Output[−]

Performs the mutable indexing (container[index]) operation.

Implementors

impl<I> IndexMut<I> for str where
    I: SliceIndex<str>, [+]

[+] Show hidden undocumented items

pub fn index_mut(&mut self, index: I) -> &mut <I as SliceIndex<str>>::Output

impl<T, I> IndexMut<I> for [T] where
    I: SliceIndex<[T]>, [+]

[+] Show hidden undocumented items

pub fn index_mut(&mut self, index: I) -> &mut <I as SliceIndex<[T]>>::Output

impl<T, I, const N: usize> IndexMut<I> for [T; N] where
    [T]: IndexMut<I>, [+]

[+] Show hidden undocumented items

pub fn index_mut(&mut self, index: I) -> &mut <[T; N] as Index<I>>::Output

impl<Buffer> IndexMut<(u8, u32, u32)> for FlatSamples<Buffer> where     Buffer: IndexMut<usize>,

impl<P, Container> IndexMut<(u32, u32)> for ImageBuffer<P, Container> where     P: Pixel + 'static,     P::Subpixel: 'static,     Container: Deref<Target = [P::Subpixel]> + DerefMut,

impl<T: Primitive> IndexMut<usize> for Rgb<T>

impl<T: Primitive> IndexMut<usize> for Bgr<T>

impl<T: Primitive> IndexMut<usize> for Luma<T>

impl<T: Primitive> IndexMut<usize> for Rgba<T>

impl<T: Primitive> IndexMut<usize> for Bgra<T>

impl<T: Primitive> IndexMut<usize> for LumaA<T>

impl<T> IndexMut<usize> for Slab<T>

impl<A: Array, I: SliceIndex<[A::Item]>> IndexMut<I> for SmallVec<A>

impl<T, P> IndexMut<usize> for Punctuated<T, P>