failable.rb

module Failable
  class Result < SimpleDelegator
    def initialize(success, object = nil)
      @success = success
      super(object)
    end
  
    def success?
      @success
    end
  
    def failure?
      !@success
    end
  end

  class Failure < StandardError
    attr_reader :object
  
    def initialize(object = nil, message = nil)
      super(message)
      @object = object
    end
  end

  def self.included(klass)
    klass.extend(ClassMethods)
  end

  def fail!(object = nil)
    self.class.fail!(object)
  end

  module ClassMethods
    def call(*args)
      Result.new(true, new(*args).call)
    rescue Failure => failure
      Result.new(false, failure.object)
    end

    def fail!(object = nil)
      fail Failure, object
    end
  end
end