some tricks in ssz

[fearlessfe]

The current way of ssz has some flaws

1. the array length is different in different preset(mainnet_preset and minimal_preset), this mainly affects encode and decode
   like HistoricalBatch, in fact the block_roots and state_roots are both array type, not Slice, but in different preset, the length is different

// 8192 in mainnet_preset and 64 in minimal_preset
pub const HistoricalBatch = struct {
    block_roots: []primitives.Root,
    state_roots: []primitives.Root,
};

maybe we can use union to solve the problem, like types in different forks

pub const BeaconBlockBody = union(primitives.ForkType) {
    phase0: phase0.BeaconBlockBody,
    altair: altair.BeaconBlockBody,
    bellatrix: bellatrix.BeaconBlockBody,
    capella: capella.BeaconBlockBody,
    deneb: deneb.BeaconBlockBody,
    electra: deneb.BeaconBlockBody,
};

2. when caculate the hashRootTree of a Slice type, we must know the limit of the slice, like attesting_indices field in
   IndexedAttestation type

pub const IndexedAttestation = struct {
    // # [Modified in Electra:EIP7549] size: MAX_VALIDATORS_PER_COMMITTEE * MAX_COMMITTEES_PER_SLOT
    attesting_indices: []primitives.ValidatorIndex,
    data: AttestationData,
    signature: primitives.BLSSignature,
};

we can add a attrs to present the limit for Slice, the field in attrs represent the limit of corresponding properties

pub const IndexedAttestation = struct {
    // # [Modified in Electra:EIP7549] size: MAX_VALIDATORS_PER_COMMITTEE * MAX_COMMITTEES_PER_SLOT
    attesting_indices: []primitives.ValidatorIndex,
    ...
    pub const attrs = struct{
         .attesting_indices = limit
   }
};

or we can consider using codegen, so some other information can be present in comments, just like tag in golang

pub const IndexedAttestation = struct {
    attesting_indices: []primitives.ValidatorIndex, // add additional information here
    data: AttestationData,
    signature: primitives.BLSSignature,
};

[GrapeBaBa]

Our goal is that building a high performance ssz lib such as https://www.youtube.com/watch?v=WIu4PGDZOqI

[GrapeBaBa]

https://github.com/ghiliweld/sszb the lib

[GrapeBaBa]

https://github.com/karalabe/ssz