Ruby Configuration pattern...

gistfile1.rb

# Hash
class MyClass
  def initialize
    @config = {
      name: "default name",
      mail: "default mail"
    }
  end

  def set_config
    yield @config
  end
end

mc = MyClass.new
mc.set_config do |config|
  config[:name] = "name changed"
  config[:mail] = "mail changed"
end
p mc #=>#<MyClass:0x7a34f0 @config={:name=>"name changed", :mail=>"mail changed"}>

# attr_accessor
class MyClass2
  attr_accessor :name, :mail

  @@default = {
    name: "default name",
    mail: "default mail"
  }

  def initialize
    @@default.each_pair {|k, v| self.send("#{k}=", v)}
  end

  def config
    return self
  end

  def set_config
    yield config
  end
end

mc2 = MyClass2.new
mc2.set_config do |sc|
  sc.name = "name changed"
  sc.mail = "main changed"
end
p mc2 #=>#<MyClass2:0x7a2c50 @name="name changed", @mail="main changed">