How to pass BufReader to another function in rust?

user_12312944 0
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new to rust, I'm asking this to hopefully understand how to work with the language better..

Heres me trying to read a file, pass the file handle to a different function and print the lines from there:

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

async fn scrape<R: BufRead>(reader: &mut R) {
    reader.lines().for_each(|line| println!(line));
}

fn main() -> io::Result<()> {
    let file = File::open("wlist.txt")?;
    let reader = BufReader::new(file);

    // print_type_of(&reader); // prints std::io::buffered::BufReader<std::fs::File>
    task::block_on(scrape(&mut reader));

    Ok(())
}

// helper functions
fn print_type_of<T>(_: &T) {
    println!("{}", std::any::type_name::<T>())
}

Would love some insights regarding what concepts i'm missing and how this should be done properly !

rust
1 Answers

This version atleast compiles, but there's no async in the playground so I coudn't add async.

You have to catch errors in scrape by using try_for_each function, inside you parse io::Result<String> via and_then. In your main you have to catch all errors explicitly, not allowed to let io::Error slip through ? operator

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

fn scrape<R: BufRead>(reader: &mut R) -> io::Result<()> {
    reader.lines()
        .try_for_each(|lineResult| lineResult.and_then(|line| Ok(println!("{}", line))))?;
    Ok(())
}

fn main() {
    //let fileResult = File::open("wlist.txt");
    //let mut file;
    //match fileResult {
    //    Ok(f) => file = f,
    //    Err(e) => println!("File open error! {}", e),
    //}
    let mut file = b"hello\nworld\nhow\nare\nyou\ndoing" as &[u8]; // no file in playground, so just a buffer
    let mut reader = BufReader::new(file);

    // print_type_of(&reader); // prints std::io::buffered::BufReader<std::fs::File>
    match scrape(&mut reader) {
        Ok(_) => println!("Scraping is done!"),
        Err(e) => println!("File read error! {}", e),
    }
}

// helper functions
fn print_type_of<T>(_: &T) {
    println!("{}", std::any::type_name::<T>())
}
user_85649990
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