libneedle-ruby1.8 1.3.0-1 / usr / share / doc / libneedle-ruby1.8 / doc / manual / parts / 03_conventional.txt

A conventional architecture will have each component instantiate its own dependencies. For example, the @Application@ would do something like this:

{{{lang=ruby,number=true,caption=A conventional application implementation
class Application
  def initialize
    @logger = Logger.new
    @authenticator = Authenticator.new
    @database = Database.new
    @view = View.new
    @session = Session.new
  end
end
}}}

However, the above is already flawed, because the @Authenticator@ and the @Session@ both need access to the @Database@, so you really need to make sure you instantiate things in the right order and pass them as parameters to the constructor of each object that needs them, like so:

{{{lang=ruby,number=true,caption=A parameterized application implementation
class Application
  def initialize
    @view = View.new
    @logger = Logger.new
    @database = Database.new( @logger )
    @authenticator = Authenticator.new( @logger, @database )
    @session = Session.new( @logger, @database )
  end
end
}}}

The problem with this is that if you later decide that @View@ needs to access the database, you need to rearrange the order of how things are instantiated in the @Application@ constructor.