Trait std::ops::Index

#[lang = "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) -> &usize {
        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.

Implementors

impl Index<Range<usize>> for str

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

Returns a 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.

Examples

let s = "Löwe 老虎 Léopard";
assert_eq!(&s[0 .. 1], "L");

assert_eq!(&s[1 .. 9], "öwe 老");

// these will panic:
// byte 2 lies within `ö`:
// &s[2 ..3];

// byte 8 lies within `老`
// &s[1 .. 8];

// byte 100 is outside the string
// &s[3 .. 100];

type Output = str

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

impl Index<Range<usize>> for String

type Output = str

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

impl Index<RangeFrom<usize>> for str

Implements substring slicing with syntax &self[begin ..].

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

Equivalent to &self[begin .. len].

type Output = str

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

impl Index<RangeFrom<usize>> for String

type Output = str

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

impl Index<RangeFull> for str

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

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

Equivalent to &self[0 .. len].

type Output = str

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

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

impl Index<RangeInclusive<usize>> for str

type Output = str

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

impl Index<RangeInclusive<usize>> for String

type Output = str

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

impl Index<RangeTo<usize>> for str

Implements substring slicing with syntax &self[.. end].

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

Equivalent to &self[0 .. end].

type Output = str

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

impl Index<RangeTo<usize>> for String

type Output = str

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

impl Index<RangeToInclusive<usize>> for str

type Output = str

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

impl Index<RangeToInclusive<usize>> for String

type Output = str

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

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

type Output = V

Important traits for &'a mut I

impl<'a, I> Iterator for &'a mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W

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.

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

type Output = V

Important traits for &'a mut I

impl<'a, I> Iterator for &'a mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W

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.

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

type Output = A

Important traits for &'a mut I

impl<'a, I> Iterator for &'a mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W

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

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

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

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

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

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

Important traits for Vec<u8>

impl Write for Vec<u8>

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