rust - Rust-从方法中获取值(value)而无需借用(计算文件行数)

Question

我在防 rust 方面还很新，我也不知道如何解决。
代码是:

let input = File::open(file_path)?;
let buffered = BufReader::new(input);

let line_count = buffered.lines().count();

 for (nr, line) in buffered.lines().enumerate() {
    print!("\rLOADED: [{}/{}]", nr, line_count);
    // do something...
}

我得到的错误:

let buffered = BufReader::new(input);
    -------- move occurs because `buffered` has type `std::io::BufReader<std::fs::File>`, which does not implement the `Copy` trait

let line_count = buffered.lines().count();
                 -------- value moved here
  
for (nr, line) in buffered.lines().enumerate() {
                  ^^^^^^^^ value used here after move

请帮助，我对此感到困惑。

Answer 1

调用BufReader::new(file_handle);会消耗file_handle，调用buffered.lines()会消耗buffered。可能有一种更有效，更聪明或更优雅的方法来执行此操作，但是如果您想首先获得完整的行数，则可以打开并遍历文件两次:

use std::fs::File;
use std::io::{self, BufRead, BufReader};

fn main() -> io::Result<()> {
    let file_path = "input.txt";
    let input = File::open(file_path)?;
    let buffered = BufReader::new(input);
    let line_count = buffered.lines().count();

    let input = File::open(file_path)?;
    let buffered = BufReader::new(input);
    for (nr, line) in buffered.lines().enumerate() {
        println!("LOADED: [{}/{}]", nr, line_count);
    }

    Ok(())
}