mismatched String type in Rust - rust

Question

I'm currently trying to learn Rust, and when I was trying to follow the official book tutorial I have encountered an error that was not described in the book.
use std::env;
use std::fs;
fn main() {
let args: Vec<String> = env::args().collect();
let config = Config::new(&args);
println!("Searching for {}", config.query);
println!("In file {}", config.filename);
println!("{:?}", args);
let contents = fs::read_to_string(config.filename)
.expect("Something went wrong reading the file");
println!("With text:\n{}", contents);
}
struct Config {
query: String,
filename: String,
}
impl Config {
fn new(args: &[String]) -> Config {
let query = &args[1].clone();
let filename = &args[2].clone();
Config { query, filename }
}
}
but I kept getting the following error from the compiler:
error[E0308]: mismatched types
--> src/main.rs:25:18
|
25 | Config { query, filename }
| ^^^^^
| |
| expected struct `std::string::String`, found `&str`
| help: try using a conversion method: `query: query.to_string()`
error[E0308]: mismatched types
--> src/main.rs:25:25
|
25 | Config { query, filename }
| ^^^^^^^^
| |
| expected struct `std::string::String`, found `&std::string::String`
| help: try using a conversion method: `filename: filename.to_string()`
error: aborting due to 2 previous errors
I have tried doing something like:
let query = &args[1].clone().to_string();
let filename = &args[2].clone().to_owned().to_string();
but it brought the same error. Finally, I have managed to solve this issue by applying the following changes:
struct Config<'a> {
query: &'a str,
filename: &'a str,
}
impl Config <'_> {
fn new(args: &[String]) -> Config {
let query = &*args[1];
let filename = &*args[2];
Config { query, filename }
}
}
My understanding is that new() could not return a struct of owned strings because values query and filename were assigned referenced values and for some reason, neither of the functions to_string(), to_owned() and clone() were not converting a referenced Sting into an owned one.
Does anyone know why I had to use referenced sices with lifetimes instead of strings?
Also, is there a way to use String type just like in the tutorial(https://doc.rust-lang.org/book/ch12-03-improving-error-handling-and-modularity.html)?

Answer 1

the query and file name type is &String, the clone method use &self, You should do like this
impl Config {
fn new(args: &[String]) -> Config {
let query = args[1].clone();
let filename = args[2].clone();
Config { query, filename }
}
}