Bit accumulator in Rust

bitacc.rs

#![feature(const_generics)]

use num::{PrimInt, Zero};

#[derive(Default)]
struct BitAcc<T: Default, const N: u8> {
    acc: T,
    n: u8,
}

impl<T: Default + PrimInt + Zero + ::std::convert::From<bool>, const N: u8> BitAcc<T, N> {
    pub fn push(&mut self, bit: bool) -> Option<T> {
        debug_assert!(self.n < N);
        self.acc = self.acc.unsigned_shl(1) | ::std::convert::From::from(bit);
        self.n += 1;
        if self.n == N {
            self.n = 0;
            let ret = Some(self.acc);
            self.acc = T::zero();
            ret
        } else {
            None
        }
    }
}

fn main() {
    let mut acc: BitAcc<u8, 1> = BitAcc::default();
    assert_eq!(acc.push(true), Some(1));
    assert_eq!(acc.push(false), Some(0));

    let mut acc: BitAcc<u8, 2> = BitAcc::default();
    assert_eq!(acc.push(true), None);
    assert_eq!(acc.push(true), Some(3));

    let mut acc: BitAcc<u8, 3> = BitAcc::default();
    assert_eq!(acc.push(true), None);
    assert_eq!(acc.push(true), None);
    assert_eq!(acc.push(true), Some(7));
}