field_struct

https://github.com/Paymentbox-com/field_struct

FieldStruct is a Ruby library for building Plain Old Ruby Objects with declared attributes that have enforced types, presence checks, and per-field validation. Each class collects its declarations into an inspectable Metadata object; types are pluggable via a registry that namespaces can extend or replace. Not a database layer, not a form object, not an ActiveModel replacement. Mirrors the AM interface shape where it helps adoption, but reuses no AM code.