How do I improve this function :
use std::{env, process::exit};fn get_grid() -> [[u8; 9]; 9] {let mut grid: [[u8; 9]; 9] = Default::default();let mut args: Vec<String> = env::args().collect();if args.len() != 10 {eprintln!("This program need 9 strings of 9 numbers between 0 and 9");exit(1);}args.remove(0);let _: Vec<_> = args.iter().enumerate().map(|(i, arg)| {let _line: Vec<_> = arg.split(' ').enumerate().map(|(j, value)| match value.parse() {Ok(x) => {grid[i][j] = x;x}Err(e) => {eprintln!("Value {} is not a valid integer [{}]", value, e);exit(1);}}).collect();}).collect();return grid;}As far as I understand .map() will, when collecting, build a new iterable ( Vec here), and return it. I don't need to have this iterable, I just want to modify an external array, and not have anything built from this iteration.
In JavaScript, there is .map, but also a .forEach that iterates on map and returns nothing. Is there any equivalent in Rust?
I could probably just use a for (index, value) in args.iter().enumerate() but I am searching a way to avoid an explicit loop, if there is one.
Best Answer
For mutating an existing data structure, using an explicit loop is the most idiomatic way to do it:
for (i, arg) in args.iter().enumerate() {for (j, value) in arg.split(' ').enumerate() {match value.parse() {Ok(x) => {grid[i][j] = x;}Err(e) => {eprintln!("Value {} is not a valid integer [{}]", value, e);exit(1);}}}}You can write this with Iterator::for_each, but it is not likely to be considered "better" by most Rust developers:
args.iter().enumerate().for_each(|(i, arg)| {arg.split(' ').enumerate().for_each(|(j, value)| match value.parse() {Ok(x) => {grid[i][j] = x;}Err(e) => {eprintln!("Value {} is not a valid integer [{}]", value, e);exit(1);}})});Regardless of which you use, you definitely should not be collecting into all those Vecs that you then throw away.