如何在 Rust 中不同大小的数组之间进行复制? [英] How do you copy between arrays of different sizes in Rust?

问题描述

如果我有两个不同大小的数组:

If I have two arrays of different sizes:

let mut array1 = [0; 8];
let array2 = [1, 2, 3, 4];

如何将 array2 复制到 array1 的前 4 个字节中?我可以使用 array1 的可变 4 字节切片，但我不确定如何或是否可以分配给它.

How would I copy array2 into the first 4 bytes of array1? I can take a mutable 4 byte slice of array1, but I'm not sure how or if I can assign into it.

推荐答案

最灵活的方式是使用迭代器依次处理每个元素:

The most flexible way is to use iterators to handle each element successively:

for (place, data) in array1.iter_mut().zip(array2.iter()) {
    *place = *data
}

.mut_iter 创建 一个 Iterator 产生 &mut u8，即指向切片/数组的可变引用.iter 与 共享引用 相同..zip 接受两个迭代器并以锁步方式遍历它们，将两者中的元素作为元组产生(并在任何一个停止时立即停止).

.mut_iter creates an Iterator that yields &mut u8, that is, mutable references pointing into the slice/array. iter does the same but with shared references. .zip takes two iterators and steps over them in lock-step, yielding the elements from both as a tuple (and stops as soon as either one stops).

如果您需要/想要在写入 place 之前对数据做任何花哨的"操作，这就是可以使用的方法.

If you need/want to do anything 'fancy' with the data before writing to place this is the approach to use.

但是，普通复制功能也作为单一方法提供，

However, the plain copying functionality is also provided as single methods,

• .copy_from，类似array1.copy_from(array2)使用.

std::slice::bytes::copy_memory，虽然您需要修剪两个数组，因为 copy_memory 要求它们的长度相同:

std::slice::bytes::copy_memory, although you will need to trim the two arrays because copy_memory requires they are the same length:

use std::cmp;
use std::slice::bytes;

let len = cmp::min(array1.len(), array2.len());
bytes::copy_memory(array1.mut_slice_to(len), array2.slice_to(len));

(如果你知道 array1 总是比 array2 长，那么 bytes::copy_memory(array1.mut_slice_to(array2.len()), array2) 也应该有效.)

(If you know that array1 is always longer than array2 then bytes::copy_memory(array1.mut_slice_to(array2.len()), array2) should also work.)

目前，bytes 版本优化得最好，直到 memcpy 调用，但希望 rustc/LLVM 改进最终会他们都这样.

At the moment, the bytes version optimises the best, down to a memcpy call, but hopefully rustc/LLVM improvements will eventually take them all to that.

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