Trait core::ops::Index

1.0.0 · source ·

pub trait Index<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);