A Rust function that accepts both String or &str and creates a copy of it

into-string.rs

// Item::new() accepts both &str and String. When called, it creates a copy of
// the parameter and uses it to initialize the returned item.
//
// The trick is in the use of the Into trait:
// https://doc.rust-lang.org/std/convert/trait.Into.html

struct Item {
    id: String
}

impl Item {
    fn new<T: Into<String>>(id: T) -> Self {
        Item { id: id.into() }
    }
}

fn main() {
    let item1 = Item::new("123");             // &str
    let item2 = Item::new("456".to_string()); // String
}