Modifying String inside a Vec<String>

[bsrodrigue]

Hello, I'm new to Rust and I want to get acquainted with Data Structures. I created a mutable String Vector and pushed some data in it. But I encounter a problem upon looping through it and changing its content:

use std::io;

fn main() {
    let mut skillset: Vec<String> = Vec::new();
    println!("Please enter your skills, enter STOP when to end:");
    loop{
        let mut input = String::new();
        io::stdin().read_line(&mut input).expect("Invalid Input");
        input = String::from(input.trim());
        if input == "STOP" {break}
        else{
            skillset.push(input);
        }
    }

    for skill in skillset{
        skill = skill.to_uppercase(); //Not working
    }

}

I want to set all String inside the Vector to uppercase.

Thanks.

[2e71828]

Can you be more specific about how it isn’t working— What does it do right now? For example, do you get a compile error or do you see incorrect output when you run the program?

[bsrodrigue]

Hello, here is the output:

error[E0384]: cannot assign twice to immutable variable `skill`
  --> src/main.rs:17:9
   |
16 |     for skill in skillset{
   |         -----
   |         |
   |         first assignment to `skill`
   |         help: make this binding mutable: `mut skill`
17 |         skill = skill.to_uppercase();
   |         ^^^^^ cannot assign twice to immutable variable

[bsrodrigue]

Oh boy, I just understood my mistake, I should have written:

for mut skill in skillset

[Knarkzel]

for skill in skillset.iter_mut() is probably more correct, but mut skill works as well.

[OptimisticPeach]

for x in my_vec consumes the Vec and you lose ownership of it. It does not change that if you do mut x since that's only changing the mutability of x. You need to do either for x in my_vec.iter_mut() or for x in &mut my_vec.

[CharlesStepp]

Boy. Perl and the Unix shells will spoil you for the real languages. Looping over a vector of Strings kicked my butt for a while today. I ended up with the logically named iter_mut() thing. Had to use to_string() to get Strings out of the str type returned from trim() and replace().

fn main() {
    let mut args:Vec<String> = env::args().collect();
    let _junk = args.remove(0);
    println!("{:?}", args);

    for arg in args.iter_mut() {
        *arg = arg.trim().replace(" ", "_").to_string();
        println!("-{}-",arg);
    }

    println!("{:?}", args);
}```

[marcianx]

You can skip and trim before accumulating them into a Vec to avoid the need to mutate args after assignment:

fn main() {
    let args: Vec<String> = env::args()
        .skip(1)
        .map(|arg| arg.trim().replace(' ', "_").to_string())
        .collect();
    println!("{:?}", args);
}

[CharlesStepp]

Excellent snippit. Thanks!