'String allocation behaving strangely

This compiles fine (from the rust lang book):

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

This does not:

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

The strange thing is that the error occurs in the println! statement:

3 | println!("{}", s); |
^ () cannot be> formatted with the default formatter

I'm new to this and trying to push the envelope a little bit, so can someone clarify this?

stringrustallocation


Solution 1:[1]

push_str() does not have a return value, i.e. it returns () which cannot be printed. So by appending it s gets type empty tuple and not String anymore.

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