Trait Bounds on Generics

// Copyright 2025 Google LLC
// SPDX-License-Identifier: Apache-2.0

use std::fmt::Display;

fn print_with_length<T: Display>(item: T) {
    println!("Item: {}", item);
    println!("Length: {}", item.to_string().len());
}

fn main() {
    print_with_length(42); // Works with integers
    print_with_length("Hello, Rust!"); // Works with strings
}

Generic functions rely on traits to determine what operations are valid for a generic type.
Without a trait bound on a generic type parameter, we don’t have access to any behavior for that type. Remove the trait bound on print_with_length and demonstrate that we’re not allowed to make assumptions about what methods it has.

ref:

https://doc.rust-lang.org/reference/trait-bounds.html