Ruby Results

example_usage.rb

args = # something

Result.try { f(args) }
  .and_then { |f_output| g(f_output) }
  .finally(
    success: proc { |g_output| rended :view },
    failure: proc { |error| flash[:error] = error.to_s }
  )

result.rb

class Result
  def self.try(&failable)
    new(nil).and_then(&failable)
  end

  def and_then(&failable)
    Result.new(failable.call(arg))
  catch error
    Failure.new(error)
  end

  def finally(success: proc {}, failure: nil)
    success.call(arg)
  end

  private
  attr_reader :arg

  def initialize(arg)
    @arg = arg
  end
end

class Failure
  def initialize(error)
    @error = error
  end

  def and_then
    self
  end

  def finally(success: nil, failure: proc {})
    failure(error)
  end

  private
  attr_reader :error
end

Is the :arg instance never used? It's initialized to nil on line 3.

Is used on line 7. It's initialized to nil since the first Result in the chain, won't need to use it.