Trait std::ops::Index

用于在不可变上下文中索引操作 (container[index])。

container[index] 实际上是 *container.index(index) 的语法糖，但仅在用作不可变值时使用。

如果请求一个可变值，则使用 IndexMut。

如果 value 的类型实现 Copy，则这允许使用诸如 let value = v[index] 之类的语法。

pub trait Index<Idx>
where
    Idx: ?Sized,
{
    type Output: ?Sized;

    // Required method
    fn index(&self, index: Idx) -> &Self::Output;
}

下面的示例在只读 NucleotideCount 容器上实现 Index，从而可以使用索引语法检索单个计数。

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);

Required Associated Types

Output

索引后返回的类型。

type Output: ?Sized

Required Methods

index

执行索引container[index]操作。

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

Panics

如果索引越界，则可能为 panic。

Implementors

String

impl Index<Range<usize>> for String

CStr

impl Index<RangeFrom<usize>> for CStr

String

impl Index<RangeFrom<usize>> for String

CString

impl Index<RangeFull> for CString

OsString

impl Index<RangeFull> for OsString

String

impl Index<RangeFull> for String

String

impl Index<RangeInclusive<usize>> for String

String

impl Index<RangeTo<usize>> for String

String

impl Index<RangeToInclusive<usize>> for String

str

impl<I> Index<I> for str
where
  I: SliceIndex<str>,

Simd<T, LANES>

impl<I, T, const LANES: usize> Index<I> for Simd<T, LANES>
where
  T: SimdElement,
  LaneCount<LANES>: SupportedLaneCount,
  I: SliceIndex<[T]>,

BTreeMap<K, V, A>

impl<K, Q, V, A> Index<&Q> for BTreeMap<K, V, A>
where
  A: Allocator + Clone,
  K: Borrow<Q> + Ord,
  Q: Ord + ?Sized,

HashMap<K, V, S>

impl<K, Q, V, S> Index<&Q> for HashMap<K, V, S>
where
  K: Eq + Hash + Borrow<Q>,
  Q: Eq + Hash + ?Sized,
  S: BuildHasher,

VecDeque<T, A>

impl<T, A> Index<usize> for VecDeque<T, A>
where
  A: Allocator,

[T]

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

Vec<T, A>

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

[T; N]

impl<T, I, const N: usize> Index<I> for [T; N]
where
	[T]: Index<I>,