little idea

gistfile1.rb

mapper = mappy do
  map :name => :username

  imap  :status => :invalid do |status|
    status == invalid
  end
end

map1 = mapper.new User, Hash
map2 = mapper.new Hash, User

user = map1.call(:name => "CiccioPasticcio", :status => "invalid")
hash = map2.call(User.new(:name => "Sbrodolino", :invalid => true))