# Trait std::ops::Index 1.0.0 [−] [src]

    pub trait Index<Idx> where Idx: ?Sized {
        type Output: ?Sized;
        fn index(&self, index: Idx) -> &Self::Output;
    }

The `Index` trait is used to specify the functionality of indexing operations like `arr[idx]` when used in an immutable context.

# Examples

A trivial implementation of `Index`. When `Foo[Bar]` happens, it ends up calling `index`, and therefore, `main` prints `Indexing!`.

use std::ops::Index; #[derive(Copy, Clone)] struct Foo; struct Bar; impl Index<Bar> for Foo { type Output = Foo; fn index<'a>(&'a self, _index: Bar) -> &'a Foo { println!("Indexing!"); self } } fn main() { Foo[Bar]; }

    use std::ops::Index;

    #[derive(Copy, Clone)]
    struct Foo;
    struct Bar;

    impl Index<Bar> for Foo {
        type Output = Foo;

        fn index<'a>(&'a self, _index: Bar) -> &'a Foo {
            println!("Indexing!");
            self
        }
    }

    fn main() {
        Foo[Bar];
    }

## Associated Types

### `type Output: ?Sized`

The returned type after indexing

## Required Methods

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

The method for the indexing (`Foo[Bar]`) operation

## Implementors

- `impl<T> Index<usize> for [T]`
- `impl<T> Index<Range<usize>> for [T]`
- `impl<T> Index<RangeTo<usize>> for [T]`
- `impl<T> Index<RangeFrom<usize>> for [T]`
- `impl<T> Index<RangeFull> for [T]`
- `impl<T> Index<RangeInclusive<usize>> for [T]`
- `impl<T> Index<RangeToInclusive<usize>> for [T]`
- `impl Index<Range<usize>> for str`
- `impl Index<RangeTo<usize>> for str`
- `impl Index<RangeFrom<usize>> for str`
- `impl Index<RangeFull> for str`
- `impl Index<RangeInclusive<usize>> for str`
- `impl Index<RangeToInclusive<usize>> for str`
- `impl<'a, K, Q, V> Index<&'a Q> for BTreeMap<K, V> where K: Ord + Borrow<Q>, Q: Ord + ?Sized`
- `impl Index<Range<usize>> for String`
- `impl Index<RangeTo<usize>> for String`
- `impl Index<RangeFrom<usize>> for String`
- `impl Index<RangeFull> for String`
- `impl Index<RangeInclusive<usize>> for String`
- `impl Index<RangeToInclusive<usize>> for String`
- `impl<T> Index<usize> for Vec<T>`
- `impl<T> Index<Range<usize>> for Vec<T>`
- `impl<T> Index<RangeTo<usize>> for Vec<T>`
- `impl<T> Index<RangeFrom<usize>> for Vec<T>`
- `impl<T> Index<RangeFull> for Vec<T>`
- `impl<T> Index<RangeInclusive<usize>> for Vec<T>`
- `impl<T> Index<RangeToInclusive<usize>> for Vec<T>`
- `impl<A> Index<usize> for VecDeque<A>`
- `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`
- `impl Index<RangeFull> for CString`
- `impl Index<RangeFull> for OsString`

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