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Trait std::ops::Index

pub trait Index<Idx>
where
    Idx: ?Sized,{
    type Output: ?Sized;

    // Required method
    fn index(&self, index: Idx) -> &Self::Output;
}

Used for indexing operations (container[index]) in immutable contexts.

container[index] is actually syntactic sugar for *container.index(index), but only when used as an immutable value. If a mutable value is requested, IndexMut is used instead. This allows nice things such as let value = v[index] if the type of value implements Copy.

Examples

The following example implements Index on a read-only NucleotideCount container, enabling individual counts to be retrieved with index syntax.

use std::ops::Index;

enum Nucleotide {
    A,
    C,
    G,
    T,
}

struct NucleotideCount {
    a: usize,
    c: usize,
    g: usize,
    t: usize,
}

impl Index<Nucleotide> for NucleotideCount {
    type Output = usize;

    fn index(&self, nucleotide: Nucleotide) -> &Self::Output {
        match nucleotide {
            Nucleotide::A => &self.a,
            Nucleotide::C => &self.c,
            Nucleotide::G => &self.g,
            Nucleotide::T => &self.t,
        }
    }
}

let nucleotide_count = NucleotideCount {a: 14, c: 9, g: 10, t: 12};
assert_eq!(nucleotide_count[Nucleotide::A], 14);
assert_eq!(nucleotide_count[Nucleotide::C], 9);
assert_eq!(nucleotide_count[Nucleotide::G], 10);
assert_eq!(nucleotide_count[Nucleotide::T], 12);

Required Associated Types

source 
type Output: ?Sized

The returned type after indexing.

Required Methods

source 
fn index(&self, index: Idx) -> &Self::Output

Performs the indexing (container[index]) operation.

Panics

May panic if the index is out of bounds.

Implementors

source 
impl Index<Range<usize>> for String
 
type Output = str
1.47.0source 
impl Index<RangeFrom<usize>> for CStr
 
type Output = CStr
source 
impl Index<RangeFrom<usize>> for String
 
type Output = str
1.7.0source 
impl Index<RangeFull> for CString
 
type Output = CStr
source 
impl Index<RangeFull> for OsString
 
type Output = OsStr
source 
impl Index<RangeFull> for String
 
type Output = str
1.26.0source 
impl Index<RangeInclusive<usize>> for String
 
type Output = str
source 
impl Index<RangeTo<usize>> for String
 
type Output = str
1.26.0source 
impl Index<RangeToInclusive<usize>> for String
 
type Output = str
source 
impl<I> Index<I> for str
where
    I: SliceIndex<str>,
 
type Output = <I as SliceIndex<str>>::Output
source 
impl<I, T, const LANES: usize> Index<I> for Simd<T, LANES>
where
    T: SimdElement,
    LaneCount<LANES>: SupportedLaneCount,
    I: SliceIndex<[T]>,
 
type Output = <I as SliceIndex<[T]>>::Output
source 
impl<K, Q, V, A> Index<&Q> for BTreeMap<K, V, A>
where
    A: Allocator + Clone,
    K: Borrow<Q> + Ord,
    Q: Ord + ?Sized,
 
type Output = V
source 
impl<K, Q, V, S> Index<&Q> for HashMap<K, V, S>
where
    K: Eq + Hash + Borrow<Q>,
    Q: Eq + Hash + ?Sized,
    S: BuildHasher,
 
type Output = V
source 
impl<T, A> Index<usize> for VecDeque<T, A>
where
    A: Allocator,
 
type Output = T
source 
impl<T, I> Index<I> for [T]
where
    I: SliceIndex<[T]>,
 
type Output = <I as SliceIndex<[T]>>::Output
source 
impl<T, I, A> Index<I> for Vec<T, A>
where
    I: SliceIndex<[T]>,
    A: Allocator,
 
type Output = <I as SliceIndex<[T]>>::Output
1.50.0source 
impl<T, I, const N: usize> Index<I> for [T; N]
where
    [T]: Index<I>,
 
type Output = <[T] as Index<I>>::Output

© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/ops/trait.Index.html