How to Use the TypeId for Runtime Type Identification

Use TypeId::of::<T>() to get a unique identifier for a type at runtime, then compare it against another TypeId to check for equality. This works for types that implement Any.

use std::any::TypeId;

fn main() {
    let id = TypeId::of::<String>();
    let is_string = id == TypeId::of::<String>();
    println!("Is String: {}", is_string);
}

For dynamic dispatch, cast a trait object to Any and call type_id() on the reference.

use std::any::{Any, TypeId};

fn main() {
    let s: &dyn Any = &String::from("hello");
    let id = s.type_id();
    let is_string = id == TypeId::of::<String>();
    println!("Is String: {}", is_string);
}

TypeId is a unique fingerprint assigned to every data type in Rust. You use it to check if a variable holds a specific type while your program is running, similar to checking a product's barcode to confirm what item it is. This is essential when working with generic code or trait objects where the exact type isn't known until execution.