Response to https://seb.wilzba.ch/b/2018/02/the-expressive-c17-coding-challenge-in-d/

expressive.rs

use std::io::prelude::*;
use std::io::{BufReader, BufWriter};
use std::fs::File;
fn main() {
    let args: Vec<String> = std::env::args().collect();
    assert_eq!(args.len(), 5, "Usage: ./tool <input.csv> <colum-name> <replacement-string> <output.csv>");
    let br        = BufReader::new(File::open(&args[1]).expect("No input file"));
    let mut lines = br.lines().map(|s | s.unwrap().split(',').map(|s| s.to_string()).collect::<Vec<_>>()).peekable();
    let col_idx   = lines.peek().and_then(|v| v.iter().position(|s| s == &args[2])).expect("Could not find column");
    let mut bw    = BufWriter::new(File::create(&args[4]).expect("Could not open output file"));
    writeln!(bw, "{}", lines.next().unwrap().join(",")).unwrap();
    lines.for_each(|mut line| {
        if line.len() > col_idx { line[col_idx] = args[3].clone() }
        writeln!(bw, "{}", line.join(",")).unwrap();
    });
    bw.flush().unwrap();
}