Trait std::ops::Index

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

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

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] 之类的好东西。

Examples

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);
Run

Required Associated Types§

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type Output: ?Sized

索引后返回的类型。

Required Methods§

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

执行索引 (container[index]) 操作。

Panics

如果索引越界,则可能为 panic。

Implementors§

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impl Index<Range<usize>> for String

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type Output = str

1.47.0 · source§

impl Index<RangeFrom<usize>> for CStr

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type Output = CStr

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impl Index<RangeFrom<usize>> for String

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type Output = str

1.7.0 · source§

impl Index<RangeFull> for CString

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type Output = CStr

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impl Index<RangeFull> for OsString

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impl Index<RangeFull> for String

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type Output = str

1.26.0 · source§

impl Index<RangeInclusive<usize>> for String

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type Output = str

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impl Index<RangeTo<usize>> for String

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type Output = str

1.26.0 · source§

impl Index<RangeToInclusive<usize>> for String

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type Output = str

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

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type Output = <I as SliceIndex<str>>::Output

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

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type Output = <I as SliceIndex<[T]>>::Output

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

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type Output = V

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

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type Output = V

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

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type Output = T

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

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type Output = <I as SliceIndex<[T]>>::Output

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

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type Output = <I as SliceIndex<[T]>>::Output

1.50.0 · source§

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

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type Output = <[T] as Index<I>>::Output