The Results of the Expressive C++17 Coding Challenge in Rust

main.rs

use std::env;
use std::io;
use std::io::{BufRead, BufReader, BufWriter, Write};
use std::fs::File;

#[derive(Debug)]
enum Error {
    Io(io::Error),
    Program(&'static str),
}

impl From<io::Error> for Error {
    fn from(e: io::Error) -> Error {
        Error::Io(e)
    }
}

impl From<&'static str> for Error {
    fn from(e: &'static str) -> Error {
        Error::Program(e)
    }
}

fn main() {
    let mut args = env::args();
    // skip the program name
    args.next().unwrap();

    let filename = args.next().unwrap();
    let column_name = args.next().unwrap();
    let replacement = args.next().unwrap();
    let output_filename = args.next().unwrap();

    let input = open_input(&filename).unwrap();
    replace_column(input, &output_filename, &column_name, &replacement).unwrap();
}

fn open_input(path: &str) -> Result<BufReader<File>, Error> {
    let f = File::open(&path)?;
    Ok(BufReader::new(f))
}

fn open_output(path: &str) -> Result<BufWriter<File>, Error> {
    let f = File::create(path)?;
    Ok(BufWriter::new(f))
}

fn replace_column(input: BufReader<File>, output_filename: &str, column: &str, replacement: &str) -> Result<(), Error> {
    let mut lines = input.lines();

    let columns = lines.next().ok_or("input is empty")??;
    let column_number = columns.split(',')
                                .position(|e| e == column)
                                .ok_or("column name doesn’t exist in the input file")?;

    let mut output = open_output(output_filename)?;
    writeln!(output, "{}", columns)?;

    for line in lines {
        let line = line?;
        let mut records: Vec<&str> = line.split(',').collect();
        records[column_number] = replacement;
        writeln!(output, "{}", records.join((",")))?;
    }

    Ok(())
}