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

The returned type after indexing.

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Required methods

Performs the indexing (container[index]) operation.

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Implementors

impl Index<Range<usize>> for str
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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

impl Index<Range<usize>> for String
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impl Index<RangeFrom<usize>> for str
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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].

impl Index<RangeFrom<usize>> for String
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impl Index<RangeFull> for str
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Implements substring slicing with syntax &self[..].

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

Equivalent to &self[0 .. len].

impl Index<RangeFull> for CString
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impl Index<RangeFull> for OsString
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impl Index<RangeFull> for String
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impl Index<RangeInclusive<usize>> for str
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impl Index<RangeInclusive<usize>> for String
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impl Index<RangeTo<usize>> for str
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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].

impl Index<RangeTo<usize>> for String
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impl Index<RangeToInclusive<usize>> for str
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impl Index<RangeToInclusive<usize>> for String
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impl<'a, K, Q, V> Index<&'a Q> for BTreeMap<K, V> where
    K: Ord + Borrow<Q>,
    Q: Ord + ?Sized
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Important traits for &'_ mut I

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
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Important traits for &'_ mut I

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