1.0.0[][src]Trait core::ops::IndexMut

#[lang = "index_mut"]
pub trait IndexMut<Idx: ?Sized>: Index<Idx> { 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

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

Implementors

impl IndexMut<Range<usize>> for str
[src]

Implements mutable substring slicing with syntax &mut self[begin .. end].

Returns a mutable slice of the given string from the byte range [begin..end).

This operation is O(1).

Panics

Panics if begin or end does not point to the starting byte offset of a character (as defined by is_char_boundary). Requires that begin <= end and end <= len where len is the length of the string.

impl IndexMut<RangeFrom<usize>> for str
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Implements mutable substring slicing with syntax &mut self[begin ..].

Returns a mutable slice of the string from byte offset begin to the end of the string.

Equivalent to &mut self[begin .. len].

impl IndexMut<RangeFull> for str
[src]

Implements mutable substring slicing with syntax &mut self[..].

Returns a mutable slice of the whole string. This operation can never panic.

Equivalent to &mut self[0 .. len].

impl IndexMut<RangeInclusive<usize>> for str
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impl IndexMut<RangeTo<usize>> for str
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Implements mutable substring slicing with syntax &mut self[.. end].

Returns a mutable slice of the string from the beginning to byte offset end.

Equivalent to &mut self[0 .. end].

impl IndexMut<RangeToInclusive<usize>> for str
[src]

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