Return a borrowed trait object by reference from a method in Rust

trait.rs

trait Volume {}

struct RawChunk; impl Volume for RawChunk {}
struct RleChunk; impl Volume for RleChunk {}
struct FileChunk; impl Volume for FileChunk {}

struct Container {
    raw: Option<RawChunk>,
    rle: Option<RleChunk>,
    file: Option<FileChunk>,
}

impl Container {
    fn get<'a>(&'a self, variant: i32) -> Option<&'a dyn Volume> {
        match variant {
            0 => self.raw.as_ref().map(|c| c as &dyn Volume),
            1 => self.rle.as_ref().map(|c| c as &dyn Volume),
            2 => self.file.as_ref().map(|c| c as &dyn Volume),
            _ => panic!(),
        }
    }
}

fn main() {
    println!("Hello, world!");
    
    let container = Container {
        raw: Some(RawChunk),
        rle: Some(RleChunk),
        file: Some(FileChunk),
    };
    
    let _ = container.get(0);
}