Enforce more structure on structs

[dignifiedquire]

I would like to propose to use something like https://github.com/go-playground/validator to allow simple validation of the content of structs, both on creation and on marshal/unmarshal.

Using the above package we could write something like this

type Block struct {
  RequiredField int `validation:"required"`
  OptionalField uint
}

func NewBlock(f1 int, f2 uint) (*Block, error) {
  out := &Block{
    RequiredField: f1,
    OptionalField: f2,
  }
  err := validate.Struct(out)
  if err != nil {
    return err
  }
  return out, nil
}

[dignifiedquire]

Looking at go-ethereum they use https://godoc.org/github.com/fjl/gencodec to do something similar, but only for marshal and unmarshal operations.

[dignifiedquire]

@phritz @whyrusleeping thoughts?

[phritz]

My reaction: this has the feeling of one of those things that seems obviously like a good at first blush (who wouldn't want valid objects?!) but that ends up encoding a rigidity that makes things hard to change. For example in tests always having to a have a fully formed Thingy even if you are only need part of it, or making it hard to change a struct once the system is launched.

BTW while it is a contentious topic, having required fields in your serialization format is generally considered harmful (eg https://github.com/google/protobuf/issues/2497). I've been bitten by it in various systems many times. I think I'd like to understand more about how we expect data and formats to change over time at various boundaries (our on-disk cache, in the network protocol if at all [what is the mechanism for adding a field?], actor & its memory, etc) before going too far down a path like this. Maybe you guys have a general strategy in your heads...

(Sorry had to delete the last comment because auto-linking caused our issue to show up on the linked issue)

[whyrusleeping]

(@phritz btw, that autolinking is only visible by people who can access this repo, its scared me before but i verified it didnt show up when i wasnt logged in)

This seems interesting. But I agree with @phritz, this is a decelerating change, not an accelerating one. We can consider something like this after we have a running testnet.