Why can't I use push_str to resolve strings3 ?

[RHSNOW]

I'd like to implement compose_me use push_str, but as the log shows, I failed.

    let a = " world!";
    let input = String::from(input);
    input.to_string().push_str(a);
    input

However, even use func push to push a char 'a' no effect.

    assertion `left == right` failed
    left: "Hello"
    right: "Hello world!"

Is there anything wrong?
Thanks!

[temanmd]

When you do to_string() here:

fn compose_me(input: &str) -> String {
    ...
    input.to_string().push_str(a);
    ...
}

then you call push_str on a new String (returned from to_string() function call), not on input.

input already has the String type, you don't have to convert it again, just remove to_string() to directly modify input.

Note that the type returned here is already a String:

let input = String::from(input);

[RHSNOW]

Thanks for your reply! It works.

    let a = " world!";
    let mut input = String::from(input);
    input.push_str(a);
    input