This presentation covers about the core concepts of ruby dynamic nature of programming that acts as the foundation for building frameworks, gems etc. This is mainly for people who are working with Ruby on Rails, as this can be used in creating code on the fly and using 'DRY' nature a lot while coding.

1. Metaprogramming
By: Rajesh Manjunath

2. Agenda
- What ?
- Concepts of metaprogramming
- Concepts that are used in rails(behind the
scene)
- hook methods

3. What is Metaprogramming ?
Code that writes code …..

4. Sharing Behavior
1) Prototypes
2) Inheritance
3) Mixins

5. Prototype Based Programming.
- Purer Form of oo programming.
- Achieved by using clone method.
- Inheriting state and behavior

6. Inheritance
- Sharing of methods between classes
- Done By Subclassing
- Pretty much used in everyday coding.

7. Modules & Mixins
- Include (as instances methods)
- extend (as class methods)

8. Dynamic Coding
- Blocks
- define_method
- bindings

9. Blocks
- {} or do-end
- block object can be created (lambda, proc,
&param)
- all are of same object proc object.

10. Lambda & Proc
- Both are proc objects.
- params passed to them.
- return

11. Bindings
- Captures the current state, and returns as an
binding object.
- This can be achieved using method “binding”.
- Used with “eval” method by passing as an
option.

12. define_method
- Used to create methods on the fly
(dynamically).
- Dry up code.
ex: find_by_*, attr_accessors etc ….

13. code-sample.
Usual code:
def user; @data[:user]; end
def email; @data[:email] end
def food; @data[:food]; end
Using define_method:
%w(user email food).each do |meth|
define_method(meth) { @data[meth.to_sym] }
end

14. Few Other Hook Methods.
- class_eval
- instance_eval
- instance_variable_(get,set)

15. class_eval & instance_eval
- These methods are used for defining class
and instance methods for a class on the
runtime.
- class_eval is used for defining instance
methods
- instance_eval is used for creating the class
methods.

16. Sample Code.
class_eval
class Person
end
Person.class_eval do
def say_hello
"Hello!"
end
end
jimmy = Person.new
jimmy.say_hello # "Hello!"
instance_eval
class Person
end
Person.instance_eval do
def human?
true
end
end
Person.human? # true

17. instance_varaible_(get,set)
- used to set the instance
- used to get the instance
methods:
instance_varaible_get
instance_varaible_set

18. Reference.
- http://www.jimmycuadra.com/posts/metaprogramming-ruby-class-eval-and-instance-eval
- http://ruby-metaprogramming.rubylearning.com/
- http://clayallsopp.com/posts/rubymotion-metaprogramming/
- Dave Thomas Videos.