将向量转换为数组并返回 [英] Convert vectors to arrays and back

问题描述

我正在尝试找出从向量转换为数组并返回的最类似于 Rust 的方式.这些宏可以工作，甚至可以用一些不安全的块来通用，但感觉都非常不像 Rust.

I am attempting to figure the most Rust-like way of converting from a vector to array and back. These macros will work and can even be made generic with some unsafe blocks, but it all feels very un-Rust like.

我将不胜感激任何输入并且不加打击，我认为这段代码远非很好或最佳.我现在只使用 Rust 几个星期，并在追逐版本和文档，所以非常感谢帮助.

I would appreciate any input and hold no punches, I think this code is far from nice or optimal. I have only played with Rust for a few weeks now and chasing releases and docs so really appreciate help.

macro_rules! convert_u8vec_to_array {
    ($container:ident, $size:expr) => {{
    if $container.len() != $size {
            None
    } else {
        use std::mem;
        let mut arr : [_; $size] = unsafe { mem::uninitialized() };
        for element in $container.into_iter().enumerate() {
            let old_val = mem::replace(&mut arr[element.0],element.1);
            unsafe { mem::forget(old_val) };
        }
        Some(arr)
        }
    }};
}

fn array_to_vec(arr: &[u8]) -> Vec<u8> {
     let mut vector = Vec::new();
     for i in arr.iter() {
         vector.push(*i);
     }
     vector
}

fn vector_as_u8_4_array(vector: Vec<u8>) -> [u8;4] {
    let mut arr = [0u8;4];
    for i in (0..4) {
        arr[i] = vector[i];
    }
    arr
}

推荐答案

代码对我来说似乎很好，尽管有一个非常重要的安全事项需要注意:当 arr 不是时，不能有恐慌t 完全初始化.在未初始化的内存上运行析构函数很容易导致未定义的行为，特别是这意味着 into_iter 和它的 next 方法不应该恐慌(我相信这是不可能的由于代码的约束，迭代器的 enumerate 和 mem::* 部分会发生恐慌).

The code seems fine to me, although there's a very important safety thing to note: there can be no panics while arr isn't fully initialised. Running destructors on uninitialised memory could easily lead be undefined behaviour, and, in particular, this means that into_iter and the next method of it should never panic (I believe it is impossible for the enumerate and mem::* parts of the iterator to panic given the constraints of the code).

也就是说，可以用一个函数来表达 replace/forget 习语:std::ptr::write.

That said, one can express the replace/forget idiom with a single function: std::ptr::write.

for (idx, element) in $container.into_iter().enumerate() {
    ptr::write(&mut arr[idx], element);
}

虽然，我会把它写成:

for (place, element) in arr.iter_mut().zip($container.into_iter()) {
    ptr::write(place, element);
}

同样，可以将一些迭代器的优点应用到 u8 专用版本:

Similarly, one can apply some iterator goodness to the u8 specialised versions:

fn array_to_vec(arr: &[u8]) -> Vec<u8> {
     arr.iter().cloned().collect()
}
fn vector_as_u8_4_array(vector: Vec<u8>) -> [u8;4] {
    let mut arr = [0u8;4];
    for (place, element) in arr.iter_mut().zip(vector.iter()) {
        *place = *element;
    }
    arr
}

虽然第一个可能更好地写成 arr.to_vec()，第二个为

Although the first is probably better written as arr.to_vec(), and the second as

let mut arr = [0u8; 4];
std::slice::bytes::copy_memory(&vector, &mut arr);
arr

虽然该功能目前不稳定，因此只能使用每晚.

Although that function is unstable currently, and hence only usable on nightly.

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