No method named `push_str` found for type `&str` after trimming a string

Question

I keep getting this error. I'm assuming it's because I shadow answer trimming it since when I comment that part out I don't get the error anymore. I don't understand why that is.

fn main() {
    let mut answer = String::new();
    let num = 40;

    if num % 2 == 0 {
        answer.push_str("fact2 ");
    }
    if num % 5 == 0 {
        answer.push_str("fact5 ");
    }

    let answer = answer.trim();
    answer.push_str("bob was here");
    println!("{}", answer);
}

error[E0599]: no method named `push_str` found for type `&str` in the current scope
  --> src/main.rs:13:12
   |
13 |     answer.push_str("bob was here");
   |            ^^^^^^^^

Answer 1

I'm assuming it's because I shadow answer trimming it

Yes. String::trim returns a &str:

pub fn trim(&self) -> &str

&str does not have the push_str method.

See also:

• Why does `name = *name.trim();` give me `expected struct `std::string::String`, found str`?
• Efficient trimming of a String
• How to "crop" characters off the beginning of a string in Rust?

Answer 2

You're right, let answer = answer.trim(); is the problem. It sets answer to have type &str, and that push_str is defined for a mutable String.

You can fix it by changing that line to:

answer = answer.trim().to_string();