Lou

Lou lets you define a pipeline of reversible transformations, that you can apply to any ruby object. It assumes nothing about your business logic or the objects that you're using. For example, you might want to define a pipeline of ImageMagick operations on an image, or a sequence of API calls. You could even use Lou as a replacement for ActiveRecord migrations.

Usage

You can define transformations in their own class like this:

require 'lou'

class HashTransformer
  extend Lou::Transformer

  # optional
  reverse_on RuntimeError

  step.up do |x|
    x.merge(a_new_key: 'this is new')
  end.down do |x|
   x.delete(:a_new_key)
   x
  end

  step.up do |x|
    x.flatten
  end.down do |x|
    Hash[*x]
  end
end

Then you can use it like this:

result = HashTransformer.apply(an_old_key: 'this is old')
# [:an_old_key, "this is old", :a_new_key, "this is new"]
original = HashTransformer.reverse(result)
# {:an_old_key=>"this is old"}

The steps are applied in the order that they're defined, when the apply method is called, with each step receiving the result of the previous one. The process can be reversed using the reverse method. Note that for each step, the input is the result of the previous step.

If reverse_on is defined, then any completed steps will be reversed if the exception specified is raised.

Transformers inherit the steps of their parent class, so it's possible to reuse steps by using inheritance.

Credits

Lou was originally inspired by Hash Mapper by Ismael Celis to be a way of transforming hashes, however, it evolved into a general purpose pipeline for arbitrary blocks of code.