CODEWITHSUNDEEP
rustrust-rustlings
Starfish
Starfish

Reputation: 51

Method `push_str` returns () instead of String

I'm trying to learn rust via rustlings and I'm encountering this weird error. I understand that it modifies self in place but why does it return a unit () instead of the modified String

impl AppendBar for String {
    // TODO: Implement `AppendBar` for type `String`.
    fn append_bar(self) -> Self {
        self.push_str(" bar")
    }
}

I tried to contain it in a variable first but I still get the same error. I was expecting that this would avoid a unit () return type.

impl AppendBar for String {
    // TODO: Implement `AppendBar` for type `String`.
    fn append_bar(self) -> Self {
       let mut contain = self;
       contain.push_str(" bar")
    }
}

Upvotes: 2

Views: 1154

Answers (2)

Rathinavelu Thiruvenkatam
Rathinavelu Thiruvenkatam

Reputation: 1

Sir, "I tried to contain it in a variable" Why? The altered variable itself can be used. If you want both will this not do?

fn main() {
   let t = "abc".to_string(); 
   let mut  s = "abc".to_string(); 
   s.push_str("def");
    println!("t = {t};; s = {s}");
    }
/* t = abc;; s = abcdef */

Upvotes: -2

Rubens Brandão
Rubens Brandão

Reputation: 421

Something like this?

impl AppendBar for String {
    fn append_bar(mut self) -> Self {
        self.push_str(" bar");
        self
    }
}

The String::push_str function don't return anything, it mutates the String in place.

So you will you need to mutate the self and return it, in two separated statements.

Upvotes: 5

Related Questions