Read this blog post first: Veil Objects to Replace DTOs

First, install it:

$ gem install veils

Then, use it like this:

require 'veil'
obj = Veil.new(obj, to_s: 'Hello, world!')

The method to_s will return Hello, world! until some other method is called and the veil is "pierced."

You can also use Unpiercable decorator, which will never be pierced: a very good instrument for data memoization.

You can also try AlterOut, which lets you modify the output of object methods on fly:

require 'alterout'
obj = AlterOut.new(obj, to_s: proc { |s| s + 'extra tail' })

There is also AlterIn decorator, to modify incoming method arguments (the result of the proc will replace the list of input arguments):

require 'alterin'
obj = AlterIn.new(obj, print: proc { |i| [i + 1] })

Keep in mind that all classes are thread-safe.

Read these guidelines. Make sure you build is green before you contribute your pull request. You will need to have Ruby 2.3+ and Bundler installed. Then:

$ bundle update
$ bundle exec rake

If it's clean and you don't see any error messages, submit your pull request.