接受任何可索引数据类型作为参数的函数

Question

我正在尝试创建一个可以接受任何接受[]运算符的类的函数。我希望它能够接受：

1. 数组通过引用或值
2. 矢量或任何其他可以索引的容器

通过一些实验，我发现我还需要一些其他的特征，如PartialOrd，PartialEq。我还需要找出容器中有多少个对象。

这是我的代码：

use std::ops::Index;
use std::iter::ExactSizeIterator;
use std::cmp::PartialEq;

pub fn find<'a, I>(input: I, key: <I as std::ops::Index<u32>>::Output) -> Option<u32>
where
    I: Index<u32> + ExactSizeIterator,
    <I as std::ops::Index<u32>>::Output: PartialEq + std::marker::Sized + std::cmp::PartialOrd,
{
    if input.len() == 0 {
        return None;
    }
    if key < input[0] || key > input[(input.len() - 1) as u32] {
        return None;
    }
    let mut index: u32 = (input.len() - 1) as u32;
    loop {
        if key < input[index] {
            index /= 2;
            continue;
        } else if input[index] < key && input[index + 1] > key {
            return None;
        } else if key > input[index] {
            index += index / 2;
            continue;
        } else if input[index] == key {
            return Some(index);
        } else {
            return None;
        }
    }
}

fn main() {
    assert_eq!(find(&[1, 2], 2), Some(1));
    assert_eq!(find([1, 2], 2), Some(1));
    assert_eq!(find(vec![1, 2], 2), Some(1));
}

它会产生以下错误：

error[E0277]: the trait bound `&[{integer}; 2]: std::ops::Index<u32>` is not satisfied
  --> src/main.rs:36:16
   |
36 |     assert_eq!(find(&[1, 2], 2), Some(1));
   |                ^^^^ the type `&[{integer}; 2]` cannot be indexed by `u32`
   |
   = help: the trait `std::ops::Index<u32>` is not implemented for `&[{integer}; 2]`
   = note: required by `find`

error[E0277]: the trait bound `&[{integer}; 2]: std::iter::ExactSizeIterator` is not satisfied
  --> src/main.rs:36:16
   |
36 |     assert_eq!(find(&[1, 2], 2), Some(1));
   |                ^^^^ the trait `std::iter::ExactSizeIterator` is not implemented for `&[{integer}; 2]`
   |
   = note: required by `find`

error[E0277]: the trait bound `[{integer}; 2]: std::ops::Index<u32>` is not satisfied
  --> src/main.rs:37:16
   |
37 |     assert_eq!(find([1, 2], 2), Some(1));
   |                ^^^^ the type `[{integer}; 2]` cannot be indexed by `u32`
   |
   = help: the trait `std::ops::Index<u32>` is not implemented for `[{integer}; 2]`
   = note: required by `find`

error[E0277]: the trait bound `[{integer}; 2]: std::iter::ExactSizeIterator` is not satisfied
  --> src/main.rs:37:16
   |
37 |     assert_eq!(find([1, 2], 2), Some(1));
   |                ^^^^ the trait `std::iter::ExactSizeIterator` is not implemented for `[{integer}; 2]`
   |
   = note: required by `find`

error[E0277]: the trait bound `std::vec::Vec<{integer}>: std::ops::Index<u32>` is not satisfied
  --> src/main.rs:38:16
   |
38 |     assert_eq!(find(vec![1, 2], 2), Some(1));
   |                ^^^^ the type `std::vec::Vec<{integer}>` cannot be indexed by `u32`
   |
   = help: the trait `std::ops::Index<u32>` is not implemented for `std::vec::Vec<{integer}>`
   = note: required by `find`

error[E0277]: the trait bound `std::vec::Vec<{integer}>: std::iter::ExactSizeIterator` is not satisfied
  --> src/main.rs:38:16
   |
38 |     assert_eq!(find(vec![1, 2], 2), Some(1));
   |                ^^^^ the trait `std::iter::ExactSizeIterator` is not implemented for `std::vec::Vec<{integer}>`
   |
   = note: required by `find`

Answer 1

我找到了实现它的方法，但有一些限制。

pub struct Validator {
    data: Vec<i32>,
}
impl<'a> From<&'a [i32; 2]> for Validator {
    fn from(input: &'a [i32; 2]) -> Self {
        Validator {
            data: input.iter().map(|c| *c).collect(),
        }
    }
}
impl From<[i32; 2]> for Validator {
    fn from(input: [i32; 2]) -> Self {
        Validator {
            data: input.iter().map(|c| *c).collect(),
        }
    }
}
impl From<Vec<i32>> for Validator {
    fn from(input: Vec<i32>) -> Self {
        Validator { data: input }
    }
}

pub fn find<T>(input: T, key: i32) -> Option<usize>
where
    T: std::convert::Into<Validator>,
    Validator: std::convert::From<T>,
{
    let input: Vec<i32> = input.into().data;

    if input.len() == 0 {
        return None;
    }
    if key < input[0] || key > input[(input.len() - 1)] {
        return None;
    }
    let mut index = input.len() - 1;
    loop {
        if key < input[index] {
            index /= 2;
            continue;
        } else if input[index] < key && input[index + 1] > key {
            return None;
        } else if key > input[index] {
            index += index / 2;
            continue;
        } else if input[index] == key {
            return Some(index);
        } else {
            return None;
        }
    }
}

fn main() {
    assert_eq!(find(&[1, 2], 2), Some(1));
    assert_eq!(find([1, 2], 2), Some(1));
    assert_eq!(find(vec![1, 2], 2), Some(1));
}

如果您需要一个接受3个或更多数字的数组的函数，则必须为每个元素数量实现它。您可以通过为验证器结构和要支持的类型实现VecDeque特性来添加对Into或自定义结构等更多结构的支持。