CODEWITHSUNDEEP
rust
akhildevelops
akhildevelops

Reputation: 611

Where does the value live after it's borrowed in the function?

Consider below code:

fn main(){
    let mut s = "Hi".to_string();
    
    s.push_str(&" foo".to_string());
    
    println!("{}",s);
}

We send reference of foo (i.e, a String not str) in push_str. But, we are not storing foo in any variable and just sending the reference.

Where does the value foo live for the reference to be valid inside of push_str.

As I'm just borrowing foo, how can I refer to foo (as a reference) later in my code i.e, after println?

Upvotes: 0

Views: 50

Answers (1)

Silvio Mayolo
Silvio Mayolo

Reputation: 70397

Rust temporaries exist until the end of the current expression, and they can even be extended if necessary. The Rust compiler effectively creates a temporary variable for that temporary that you never see. This

s.push_str(&" foo".to_string());

is semantically equivalent to

{
  let tmp = " foo".to_string();
  s.push_str(&tmp);
}

Upvotes: 2

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