Great work @wingyplus, this is some inspiring stuff.

One concern I had though with this approach is that having a defstruct-like DSL that looks like Kernel.defstruct but behaves differently can be confusing.

Your work inspired me to experiment with Sigil, a proof-of-concept DSL for defining nested structs and validating external data using Zoi:

defmodule Post do
  use Sigil.Schema

  schema do
    field :title, Zoi.string()

    field :image, Image do
      field :url, Zoi.string()
      field :blurhash, Zoi.string()

      field :metadata, Metadata do
        field :size, Zoi.integer() |> Zoi.optional()
        field :format, Zoi.string() |> Zoi.optional()
      end
    end
  end
end

I’m still iterating and may try more compact forms for types like:

field :age, :integer, coerce: true

This has been a great way to learn macros and DSL design, and aims to complement(and obviously heavily inspired by) Ecto. Whereas Ecto handles data mapping and persistence at the external data/application(and database) layer, validation libraries like zoi and the likes and thus Sigil aim to provide a layer that works great for things like wrapping external api’s into client libraries and doing validation and egornomic casting into elixir constructs.

Thanks again—I hope others find it interesting.

awesome @wingyplus

You can leverage some of the helpers on the Zoi Struct module as @byu mentioned. I personally decided to not add any macros into the library (unless strictly necessary like infering type specs) but I added these helpers for anyone who wishes to extend it.
Thanks for using Zoi, awesome to see this

I’m so happy libraries like Zoi seem to catch on and inspire extension (infant adoption steps, but still).

They complement my way of thinking really well!