Newly added in version 1.38 std::any::type_name!!
use std::any::type_name;
fn type_of<T>(_: T) -> &'static str {
type_name::<T>()
}
fn main() {
let x = 21;
let y = 2.5;
println!("{}", type_of(&y));
println!("{}", type_of(x));
}