copy.rs

#[derive(Debug, Clone, Copy)]
enum MyRef<'a> {
  String(&'a str),
  Bytes(&'a [u8]),
}

impl<'a> Into<&'a str> for MyRef<'a> {
    fn into(self) -> &'a str {
        if let MyRef::String(s) = self {
            s
        } else {
            panic!("not a str")
        }
    }
}

impl<'a> Into<&'a [u8]> for MyRef<'a> {
    fn into(self) -> &'a [u8] {
        if let MyRef::Bytes(b) = self {
            b
        } else {
            panic!("not a bytes")
        }
    }
}

fn main() {
    let mut owned = String::new();
    owned.push_str("Hello");
    owned.push_str(" World");
    owned.push('!');

    let strref: &str = &owned;
    
    let bytes = owned.as_bytes();
    
    let items = vec![
        MyRef::String(strref),
        MyRef::Bytes(bytes),
    ];
    
    println!("{:?}", items);
    
    let bytescopy: &[u8] = items[1].into();
    let strcopy: &str = items[0].into();
    
    // copy just copies the memory of the structure
    // the bytes and str are not actually copied, just their pointers
    println!("{:p} == {:p}", strref, strcopy);
    println!("{:p} == {:p}", bytes, bytescopy);
}