Returning a string from a method in Rust

Question

Editor's note: The syntax in this question predates Rust 1.0 and the 1.0-updated syntax generates different errors, but the overall concepts are still the same in Rust 1.0.

I have a struct T with a name field, I'd like to return that string from the name function. I don't want to copy the whole string, just the pointer:

struct T {
     name: ~str,
}

impl Node for T {
     fn name(&self) -> &str { self.name }
     // this doesn't work either (lifetime error)
     // fn name(&self) -> &str { let s: &str = self.name; s }
}

trait Node {
     fn name(&self) -> &str;
}

Why is this wrong? What is the best way to return an &str from a function?

Answer 1

You have to take a reference to self.name and ensure that the lifetimes of &self and &str are the same:

struct T {
    name: String,
}

impl Node for T {
    fn name<'a>(&'a self) -> &'a str {
        &self.name
    }
}

trait Node {
    fn name(&self) -> &str;
}

You can also use lifetime elision, as shown in the trait definition. In this case, it automatically ties together the lifetimes of self and the returned &str.

Take a look at these book chapters:

• References and borrowing
• Lifetime syntax