Object Initialization and Configuration

• Parameters to initialize:
  • good if there are only a few common parameters that are used almost everytime

file = File.new( "foo.txt", "r" )

• Hash parameter to initialize:
  • nice if there are only a few parameters and most parameters have defaults
  • nice because it names the parameters (more verbose)
  • order of parameters doesn't matter

db = Ramen.new ( :connection => my_connection, :engine => Sql2005 )

• Context block
  • useful when there are many configuration options needed
  • can operate like a DSL by providing methods on the block parameter (conf in the example below)
  • can easily configure multiple closures
  • provides a lexical scope where the configuration object is valid, but the obj being created is not ready for use.

obj = SomeObject.new do | conf |
  conf.option1 = 'foo'
  conf.option2 = bar
  conf.select :everything
  conf.blockOne { |a| puts a }
  conf.blockTwo { |a| pp a }
end

• Properties
  • poor style
    • not clear when the obj is ready for use.
    • configuration could get changed later by accidentally setting config properties at the wrong time.

obj = SomeObject.new
obj.option1 = 'foo'
obj.option2 = bar
obj.select :everything

• Prototype
• not commonly used
• useful when creating lots of similar objects
• automatically calls initialize_copy method on the new object
  

obj = another_object.clone   # copies everything: state, singleton methods, etc
obj = another_object.dup     # copies state and tainted?

•  Allocate
• see What's Shiny and New in Ruby 1.8.0? (example below is from this article)
  
• bypasses the constructor

o = Object::const_get( class_name ).allocate
class_props.each_pair { |k,v| o.instance_eval "@#{k} = v" }