How can I get bit value at positioned index in Rust?

Question

I am trying to execute the below program.

fn main() {
    let a: u8 = 0b00000001;
    let b: u8 = 0b10101010;
    let c: u8 = 0b00001111;
    let length = a.count_ones() + a.count_zeros();
    for n in 0..length {
        println!("{}", a[n]);
        println!("{}", b[n]);
        println!("{}", c[n]);
    }
}

But I am getting error[E0608]: cannot index into a value of type `u8`

Answer 1

Rust doesn't provide indexes into individual bits of an integer. You need to use bitwise operators instead:

This will count from the right (least to most significant bits):

fn main() {
    let a: u8 = 0b00000001;
    let b: u8 = 0b10101010;
    let c: u8 = 0b00001111;
    let length = a.count_ones() + a.count_zeros();
    for n in 0..length {
        println!("{}", a >> n & 1);
        println!("{}", b >> n & 1);
        println!("{}", c >> n & 1);
    }
}

The reason why this isn't provided is that the Index trait is defined like this:

pub trait Index<Idx>
where
    Idx: ?Sized,
{
    type Output: ?Sized;
    fn index(&self, index: Idx) -> &Self::Output;
}

index() returns a reference, but references are always to a byte address; you can't make a reference to a single bit.

---

Depending on your actual use case, you may also be interested in one of these crates:

• bitfield
• bitvec.