add "Create random passwords from a set of allowed characters" example

[budziq]

Given a set of allowed ASCII chars, generate a set of passwords with given length.

Use rand or ring (the ring will most likely be a better idea although the implementation will be more involved) crate

cc #227

Thanks for the idea @Phaiax !

[Pratham567]

I can assist you in this.

[devesh-verma]

@budziq can I work on this ?

[budziq]

oh sorry I have missed that the example is taken. Please see if anything else interests you @devshiva619

[devesh-verma]

@budziq thats okay :)

[budziq]

Hi @Pratham567 do you need any help with this example?

[anna-liao]

@budziq I am interested in working on this issue. I couldn't find an example for using ring. Here is my first try at writing an example with rand, but I am getting an error error: use of unstable library feature 'ascii_ctype' (see issue #39658).

extern crate rand;

use std::ascii::AsciiExt;
// alphanumeric and punctuation are allowed, length 30 password
fn main() {
    let mut passwd: Vec<char>;
    let mut index = 0;
    
    while index < 30 {
        let randchar = rand::random::<char>();
        if randchar.is_ascii_alphanumeric() || randchar.is_ascii_punctuation() {
            passwd[index] = randchar;
            index += 1;
        }
    }
    
    println!("{:?}", passwd);
}

[budziq]

@anna-liao you are trying to use nightly feature 'ascii_ctype' on a stable compiler so it does not work :)

I'd suggest not to over-think the example and just use https://doc.rust-lang.org/rand/rand/trait.Rng.html#method.gen_ascii_chars or if we really want to include the punctuation then we can have minimal reimplementation of it like in https://doc.rust-lang.org/rand/src/rand/lib.rs.html#677.

On a side note, please post a PR even if it is not working, it is easier to discuss then 👍