Add validations to constrain the return from execute

[ghost]

It would be very useful to be able to constrain the return type of execute.

Ideally it can be defined in a block like so:

class GetFavToppings < ActiveInteraction::Base

  returns do
     string :topping_name
     integer :weight
  end

  def execute

      prepare_return do |p|
         p.add(:topping_name, 'peppers')
         p.add(:weight, 10)
      end
  end

end

[tfausak]

This is interesting! I like this idea. I have a few questions, though:

1. What should happen if the return value does not match the expected type? I guess adding an error to :base would make the most sense.
2. Invalid interactions will soon be able to return things too. (See issue Return a result even when validation fails? #168 for some info about that.) Should those return values be type checked?

If you need this functionality now, you should be able to wrap execute with a contract. I am a fan of contracts.ruby, which would look like this:

Contract None => Num
def execute
  42
end

[tfausak]

I am willing to continue discussing this with you, but I do not think that we will add this feature to ActiveInteraction. If you want this behavior, it is possible to use another library (like contracts.ruby) to get it done. ActiveInteraction is mostly concerned with validating inputs. It is common for interactions to have no useful return type at all.