How to Use Box<dyn Error> for Error Handling in Rust

Use Box<dyn Error> as the error type in your function's Result to handle multiple error types without defining a custom enum.

use std::error::Error;
use std::fs::File;

fn run() -> Result<(), Box<dyn Error>> {
    let _greeting_file = File::open("hello.txt")?;
    Ok(())
}

This pattern allows the ? operator to automatically convert any error implementing the Error trait into a Box<dyn Error>, simplifying error propagation in functions like run or main.

Box is a flexible container that lets your function return any kind of error without you having to list them all out. It works like a universal adapter that fits any error type, so you can focus on your logic instead of managing error definitions. Use this when you need to pass errors up the call stack without writing repetitive conversion code.