[SOLVED] How to replace the content of a String variable after it has been created?

How to replace the content of a String variable after it has been created?

I found two different ways to do it; but as a code reader, neither of them clearly describes what we want to do (simply setting the string content); I would have expected something like s.set("hello"):

fn main() {
    let mut s = String::from("hi");
    s.clear();
    s.push_str("hello");
    println!("{}", s);

    let mut s = String::from("hi");
    s.replace_range(.., "hello");
    println!("{}", s);
}

Is there a more readable way to do it? It is such a straightforward task that I'm surprised there is no shortcut method for it.

My goal is to keep as much efficiency as possible. I'd like to keep the actual capacity if possible, copy the new string content into the existent allocated zone and update the string size.

Solution

I would use String::replace_range:

fn main() {
    let mut s: String = String::from("alpha");
    println!("{}", s);

    s.replace_range(.., "beta");
    println!("{}", s);
}

If you truly dislike this, you can create an extension trait:

fn main() {
    let mut s: String = String::from("alpha");
    println!("{}", s);

    s.set("beta");
    println!("{}", s);
}

trait StringSetExt {
    fn set(&mut self, s: &str);
}

impl StringSetExt for String {
    fn set(&mut self, s: &str) {
        self.replace_range(.., s);
    }
}

It is such a straightforward task that I'm surprised there is no shortcut method for it.

I honestly don't think I've ever seen anyone want to do this in the ~5 years I've been doing Rust, and I think it's rarely worth it from a performance point of view.

Instead, I think it's more likely that the caller has already allocated some memory that they don't care about. In that case, I'd accept the string from them:

struct Person(String);

impl Person {
    fn set_name(&mut self, s: impl Into<String>) {
        self.0 = s.into();
    }
}

fn main() {
    let mut p = Person(String::new());
    p.set_name("alpha");
    p.set_name(String::from("beta"));
}