std::ops::Index - Rust
Description: API documentation for the Rust `Index` trait in crate `std`.
Keywords: rust, rustlang, rust-lang, Index

# 1.0.0[−][src]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) -> &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);Run

## Associated Types

### `type Output: ?Sized`

The returned type after indexing.

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## Required methods

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

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

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## Implementations on Foreign Types

### `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`

####
ⓘImportant traits for &'_ mut F

### Important traits for &'_ mut F

`impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, R: Read + ?Sized> Read for &'_ mut Rimpl<'_, W: Write + ?Sized> Write for &'_ 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`.

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## Implementors

### `impl Index<Range<usize>> for String`[src]

#### `type Output = str`

#### `fn index(&self, index: Range<usize>) -> &str`[src]

### `impl Index<RangeFrom<usize>> for String`[src]

#### `type Output = str`

#### `fn index(&self, index: RangeFrom<usize>) -> &str`[src]

### `impl Index<RangeFull> for CString`[src]

#### `type Output = CStr`

#### `fn index(&self, _index: RangeFull) -> &CStr`[src]

### `impl Index<RangeFull> for OsString`[src]

#### `type Output = OsStr`

#### `fn index(&self, _index: RangeFull) -> &OsStr`[src]

### `impl Index<RangeFull> for String`[src]

#### `type Output = str`

#### `fn index(&self, _index: RangeFull) -> &str`[src]

### `impl Index<RangeInclusive<usize>> for String`[src]

#### `type Output = str`

#### `fn index(&self, index: RangeInclusive<usize>) -> &str`[src]

### `impl Index<RangeTo<usize>> for String`[src]

#### `type Output = str`

#### `fn index(&self, index: RangeTo<usize>) -> &str`[src]

### `impl Index<RangeToInclusive<usize>> for String`[src]

#### `type Output = str`

#### `fn index(&self, index: RangeToInclusive<usize>) -> &str`[src]

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

#### `type Output = V`

####
ⓘImportant traits for &'_ mut F

### Important traits for &'_ mut F

`impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, R: Read + ?Sized> Read for &'_ mut Rimpl<'_, W: Write + ?Sized> Write for &'_ mut W`
`fn index(&self, key: &Q) -> &V`[src]

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

# Panics

Panics if the key is not present in the `BTreeMap`.

### `impl<'_, K, Q: ?Sized, V, S> Index<&'_ Q> for std::collections::HashMap<K, V, S> where
K: Eq + Hash + Borrow<Q>,
Q: Eq + Hash,
S: BuildHasher,` [src]

#### `type Output = V`

####
ⓘImportant traits for &'_ mut F

### Important traits for &'_ mut F

`impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, R: Read + ?Sized> Read for &'_ mut Rimpl<'_, W: Write + ?Sized> Write for &'_ mut W`
`fn index(&self, key: &Q) -> &V`[src]

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>`[src]

#### `type Output = A`

####
ⓘImportant traits for &'_ mut F

### Important traits for &'_ mut F

`impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, R: Read + ?Sized> Read for &'_ mut Rimpl<'_, W: Write + ?Sized> Write for &'_ mut W`
`fn index(&self, index: usize) -> &A`[src]

### `impl<I> Index<I> for str where
I: SliceIndex<str>,` [src]

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

#### `fn index(&self, index: I) -> &<I as SliceIndex<str>>::Output`[src]

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

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

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

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

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

####
ⓘImportant traits for Vec<u8>

### Important traits for Vec<u8>

`impl Write for Vec<u8>`
`fn index(&self, index: I) -> &<Vec<T> as Index<I>>::Output`[src]

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