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
impl Index<RangeFrom<usize>> for CStr
type Output = CStr
impl Index<RangeFrom<usize>> for String
type Output = str
impl Index<RangeFull> for CString
type Output = CStr
impl Index<RangeFull> for OsString
type Output = OsStr
impl Index<RangeFull> for String
type Output = str
impl Index<RangeInclusive<usize>> for String
type Output = str
impl Index<RangeTo<usize>> for String
type Output = str
impl Index<RangeToInclusive<usize>> for String
type Output = str
type Output = V
impl<I> Index<I> for str where
I: SliceIndex<str>,
type Output = <I as SliceIndex<str>>::Output
type Output = V
type Output = T
impl<T, I> Index<I> for [T] where
I: SliceIndex<[T]>,
type Output = <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
type Output = <[T] as Index<I>>::Output
© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/ops/trait.Index.html