..= for inclusive ranges - The Edition Guide

# `..=` for inclusive ranges

Since well before Rust 1.0, you’ve been able to create exclusive ranges with `..` like this:

    for i in 1..3 {
        println!("i: {}", i);
    }

This will print `i: 1` and then `i: 2`. Today, you can now create an inclusive range, like this:

    #![allow(unused_variables)]
    fn main() {
    for i in 1..=3 {
        println!("i: {}", i);
    }
    }

This will print `i: 1` and then `i: 2` like before, but also `i: 3`; the three is included in the range. Inclusive ranges are especially useful if you want to iterate over every possible value in a range. For example, this is a surprising Rust program:

    fn takes_u8(x: u8) {
        // ...
    }

    fn main() {
        for i in 0..256 {
            println!("i: {}", i);
            takes_u8(i);
        }
    }

What does this program do? The answer: it fails to compile. The error we get when compiling has a hint:

    error: literal out of range for u8
     --> src/main.rs:6:17
      |
    6 |     for i in 0..256 {
      |                 ^^^
      |
      = note: #[deny(overflowing_literals)] on by default

That’s right, since `i` is a `u8`, this overflows, and the compiler produces an error.

We can do this with inclusive ranges, however:

    fn takes_u8(x: u8) {
        // ...
    }

    fn main() {
        for i in 0..=255 {
            println!("i: {}", i);
            takes_u8(i);
        }
    }

This will produce those 256 lines of output you might have been expecting.