Could Ruby Structs be useful to ActiveRecord?

The DAO pattern is totally different than the ActiveRecord pattern, so
you probably won't see anything like this happen inside of AR itself.
Other ORMs may do something like this, though.

If your model is just a struct, then it has no 'domain' methods...

What do you mean for ‘domain’ methods? Do you mean validations, etc? They can be implemented; the model could be a sort of “struct on steroids”… something like this:

module ActiveRecord
class Struct < ::Struct
def self.find
end
def self.all
end
# other various implementations
end
class StructFor
def
# retrieve table column names
ActiveRecord:::Struct.new(*table_column_names)
end
end
end

model:
class User < ActiveRecord::StructFor[:users] # this returns ActiveRStruct.new(:firstname, :lastname, :active)

def before_save
# …
end

end

Yeah, you'd _have_ to do something like that. Then you're not
implementing the ActiveRecord pattern anymore, so I don't think it'd
really be appropriate.