How do I print the type of a variable in Rust?

Question

I have the following:

let mut my_number = 32.90;

How do I print the type of my_number?

Using type and

Answer 1

You can use the std::any::type_name function. This doesn't need a nightly compiler or an external crate, and the results are quite correct:

fn print_type_of(_: &T) {
    println!("{}", std::any::type_name::())
}

fn main() {
    let s = "Hello";
    let i = 42;

    print_type_of(&s); // &str
    print_type_of(&i); // i32
    print_type_of(&main); // playground::main
    print_type_of(&print_type_of::); // playground::print_type_of
    print_type_of(&{ || "Hi!" }); // playground::main::{{closure}}
}

Be warned: as said in the documentation, this information must be used for a debug purpose only:

This is intended for diagnostic use. The exact contents and format of the string are not specified, other than being a best-effort description of the type.

If you want your type representation to stay the same between compiler versions, you should use a trait, like in the phicr's answer.