Experiments with generic-array and BeaconState

generic_beacon_state.rs

use generic_array::*;
use std::marker::PhantomData;
use typenum::Unsigned;
use typenum::{U1024, U4096, U512, U8192};

type Hash = [u8; 32];
type Crosslink = u64;

trait FixedArray<T> {
    // Not using `std::Default` for brevity.
    fn default() -> Self;

    // Bogus method for demonstration.
    fn num_elems(&self) -> usize;
}

impl<T: Default, N> FixedArray<T> for GenericArray<T, N>
where
    N: ArrayLength<T>,
{
    fn default() -> Self {
        <Self as Default>::default()
    }

    fn num_elems(&self) -> usize {
        N::to_usize()
    }
}

struct GenericBundle<R, C> {
    _nightmares: PhantomData<(R, C)>,
}

trait Bundle {
    type RandaoMixesArray: FixedArray<Hash>;
    type CrosslinkArray: FixedArray<Crosslink>;
}

impl<R, C> Bundle for GenericBundle<R, C>
where
    R: ArrayLength<Hash>,
    C: ArrayLength<Crosslink>,
{
    type RandaoMixesArray = GenericArray<Hash, R>;
    type CrosslinkArray = GenericArray<Crosslink, C>;
}

type BigBundle = GenericBundle<U8192, U1024>;
type SmallBundle = GenericBundle<U4096, U512>;

struct BeaconState<T: Bundle> {
    slot: u64,
    lastest_randao_mixes: Box<T::RandaoMixesArray>,
    current_crosslinks: Box<T::CrosslinkArray>,
}

type BigBoiState = BeaconState<BigBundle>;
type SmallBoiState = BeaconState<SmallBundle>;

impl<T: Bundle> BeaconState<T> {
    pub fn genesis() -> Self {
        Self {
            slot: 0,
            lastest_randao_mixes: Box::new(T::RandaoMixesArray::default()),
            current_crosslinks: Box::new(T::CrosslinkArray::default()),
        }
    }
}

fn print_slot<T: Bundle>(state: &BeaconState<T>) {
    println!(
        "num randao: {}, num_crosslinks: {}",
        state.lastest_randao_mixes.num_elems(),
        state.current_crosslinks.num_elems()
    )
}

fn main() {
    let nr = 8192;
    if nr == 4096 {
        let state = SmallBoiState::genesis();
        print_slot(&state);
    } else {
        let state = BigBoiState::genesis();
        print_slot(&state);
    };
}