Macro match_metacall_value_ref 

macro_rules! match_metacall_value_ref {
    ( $any:expr, { $( $var:ident : $type:ty => $arm:expr ),*, _ => $default:expr } ) => { ... };
}

Same as match_metacall_value but gives a reference. For example: …

use metacall::{metacall_untyped_no_arg, match_metacall_value_ref};

let value = metacall_untyped_no_arg("returns_string_or_number").unwrap();
match_metacall_value_ref!(value, {
    str: String => str.to_owned(),
    num: i16 => num.to_string(),
    num: i32 => num.to_string(),
    num: i64 => num.to_string(),
    num: f32 => num.to_string(),
    num: f64 => num.to_string(),
    _ =>  String::from("Invalid output!")
});