Cow

[wuyuedefeng]

use std::borrow::Cow;
fn main() {
    // `Cow<'_, str>` can be an owned `String` or a borrowed `&str`
    pub trait Func1tr {
        fn gets(a: &str) -> Cow<'_, str>;
    }
    
    pub struct Func;
    impl Func1tr for Func {
        // Returns an owned `String`
        fn gets(a: &str) -> Cow<'_, str> {
            let mut m = String::from("aa");
            m.push_str(a);
            m.into()
        }
    }

    pub struct StrReturner;
    impl Func1tr for StrReturner {
        // Returns a borrowed `&str`
        fn gets(a: &str) -> Cow<'_, str> {
            let offset = a.chars().next().map(char::len_utf8).unwrap_or(0);
            let s = &a[offset..];
            s.into()
        }
    }
    

    let m = "sdsd";
    
    let c = Func::gets(m);
    println!("{}", c);
    
    let c = StrReturner::gets(m);
    println!("{}", c);
}