How to sort ReadDir iterator

Question

I can display a directory list like this:

use std::fs;

fn main() {
    let paths = fs::read_dir("./").unwrap();
    for path in paths {
        println!("Name: {}", path.unwrap().path().display())
    }
}

Can I sort the ReadDir iterator before iteration? The directory names are date-like numbers like 201610131503. I read the documentation for ReadDir but I did not find a built-in function for this. Maybe I do not know how to search?

Answer 1

ReadDir only reads one entry at a time, so it can't sort it before iterating. There is no sorted readdir system call (at least not on the platforms I know of, which means there can't be a portable one).

So the only option is to read into a Vec and sort there:

use std::fs;

fn main() {
    let mut paths: Vec<_> = fs::read_dir("/").unwrap()
                                              .map(|r| r.unwrap())
                                              .collect();
    paths.sort_by_key(|dir| dir.path());
    for path in paths {
        println!("Name: {}", path.path().display())
    }
}

Answer 2

Can I sort the ReadDir iterator before iteration?

Basically, no. On macOS and Linux, the readdir_r function is used. This is not guaranteed to return in any specific order. Generally, it will return in the order that is fastest / easiest for the filesystem, which could change every time you call it.

You will need to collect the items, sort them, then re-iterate.