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) -> &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);Run

## 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`

[src]

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];Run

#### `type Output = str`

####

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

[src]

###

`impl Index<Range<usize>> for String`

[src]

#### `type Output = str`

####

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

[src]

###

`impl Index<RangeFrom<usize>> for str`

[src]

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`

[src]

###

`impl Index<RangeFrom<usize>> for String`

[src]

#### `type Output = str`

####

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

[src]

###

`impl Index<RangeFull> for str`

[src]

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`

[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 str`

[src]

#### `type Output = str`

####

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

[src]

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`

[src]

###

`impl Index<RangeTo<usize>> for String`

[src]

#### `type Output = str`

####

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

[src]

###

`impl Index<RangeToInclusive<usize>> for str`

[src]

#### `type Output = str`

####

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

[src]

###

`impl Index<RangeToInclusive<usize>> for String`

[src]

#### `type Output = str`

####

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

[src]

###

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

[src]

#### `type Output = V`

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ 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`

[src]

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,`

[src]

#### `type Output = V`

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ 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`

[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 I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ 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`

[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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