Ruby Metaprogramming
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The document discusses metaprogramming, which is the practice of writing code that generates or manipulates other code. Key concepts include prototypes, inheritance, and mixins, with examples like using 'define_method' for dynamic coding and 'class_eval' and 'instance_eval' for runtime method definitions. It also references various resources for further learning about metaprogramming in Ruby.
![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](https://image.slidesharecdn.com/ruby-metaprogramming-140606014907-phpapp02/85/Ruby-Metaprogramming-13-320.jpg)
Ruby Metaprogramming
- 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, ¶m) - 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.