Trait std::ops::Index

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

Associated Types

type Output: ?Sized

The returned type after indexing.

Required methods

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

Performs the indexing (container[index]) operation.

Panics

May panic if the index is out of bounds.

Implementors

impl Index<Range<usize>> for String

type Output = str

pub fn index(&self, index: Range<usize>) -> &str

impl Index<RangeFrom<usize>> for CStr

type Output = CStr

fn index(&self, index: RangeFrom<usize>) -> &CStr

impl Index<RangeFrom<usize>> for String

type Output = str

pub fn index(&self, index: RangeFrom<usize>) -> &str

impl Index<RangeFull> for CString

type Output = CStr

fn index(&self, _index: RangeFull) -> &CStr

impl Index<RangeFull> for OsString

type Output = OsStr

fn index(&self, _index: RangeFull) -> &OsStr

impl Index<RangeFull> for String

type Output = str

pub fn index(&self, _index: RangeFull) -> &str

impl Index<RangeInclusive<usize>> for String

type Output = str

pub fn index(&self, index: RangeInclusive<usize>) -> &str

impl Index<RangeTo<usize>> for String

type Output = str

pub fn index(&self, index: RangeTo<usize>) -> &str

impl Index<RangeToInclusive<usize>> for String

type Output = str

pub fn index(&self, index: RangeToInclusive<usize>) -> &str

impl<'_, K, Q, V> Index<&'_ Q> for BTreeMap<K, V> where
    K: Borrow<Q> + Ord,
    Q: Ord + ?Sized, 

pub fn index(&self, key: &Q) -> &V

Returns a reference to the value corresponding to the supplied key.

Panics

Panics if the key is not present in the BTreeMap.

type Output = V

impl<A> Index<usize> for VecDeque<A>

type Output = A

pub fn index(&self, index: usize) -> &A

impl<I> Index<I> for str where
    I: SliceIndex<str>, 

type Output = <I as SliceIndex<str>>::Output

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

impl<K, Q: ?Sized, V, S> Index<&'_ Q> for HashMap<K, V, S> where
    K: Eq + Hash + Borrow<Q>,
    Q: Eq + Hash,
    S: BuildHasher, 

fn index(&self, key: &Q) -> &V

Returns a reference to the value corresponding to the supplied key.

Panics

Panics if the key is not present in the HashMap.

type Output = V

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

type Output = <I as SliceIndex<[T]>>::Output

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

impl<T, I, A> Index<I> for Vec<T, A> where
    I: SliceIndex<[T]>,
    A: Allocator, 

type Output = <I as SliceIndex<[T]>>::Output

pub fn index(&self, index: I) -> &<Vec<T, A> as Index<I>>::Output

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

type Output = <[T] as Index<I>>::Output

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