Hey Everyone,
Vinsol is proudly taking charge to spread Rubyism in delhi and to grow the Ruby & Rails communities here in New Delhi, India. We are organizing delhi.rb meetups around once every month, the meetup is all about ruby and rails as well. The meetup was on 19th July 2007 was our second meetup, first was on 22nd June 2007.

Manik presenting SOLR

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Me presenting Some Advance Ruby Skills

More photos here.

It was really a nice experience attending the meetup, sharing the ruby/rails thoughts and upcoming features. It helps keeping yourself up-to-date with the latest trends in this technology domain at least in Ruby and Rails(what else m talking except ruby :D). So, there were two presentations in the meetup — first Manik presented Full text search implementation for Rails using SOLR(it was really an interesting presentation, i got SOLR learning for free, thanks Manik :)), second I presented Some Advance Ruby Skills which i am going to share in this post too. Though in the first meetup I presented Caching on RubyOnRails but i haven’t posted here…

Some Advance Ruby Skills

1.) Everything is object

A popular phrase about Ruby, “Everything is Object”. At the root of the ruby it is Object. Everything we define in ruby is object. Even the classes we define are actually object. A class defined with class ClassName; end is actually an object of the class Class.
The Object keeps the record of whatever class or module we define. We can justify it as

<br /> class Klass<br /> end<br /> Object.constants.include?(”Klass”) # => true<br />

2.) module_eval

Use module_eval to define instance and class methods of a class at runtime, when you are outside the class.
example 1
defining an instance method

<br /> class C<br /> end</p> <p> C.module_eval do<br /> define_method :wish do<br /> p “hello instance method”<br /> end<br /> end</p> <p> c = C.new<br /> c.wish # => hello instance method<br />

example 2
defining a class method

<br /> class C<br /> end</p> <p> C.module_eval do<br /> class << self<br /> define_method :wish do<br /> p "hello class method"<br /> end<br /> end<br /> end</p> <p> C.wish # => hello class method<br />

example 3
another form of using module_eval
when method body is available as a String object

<br /> class D<br /> class << self<br /> def method_body<br /> ret =<<-EOS<br /> def wish<br /> p "hello, supplied as String object"<br /> end<br /> EOS<br /> end<br /> end</p> <p> class C<br /> end</p> <p> c = C.new</p> <p> c.class.module_eval(D.method_body)</p> <p> c.wish # => hello, supplied as String object<br /> end<br />

3.) alias_method

It is NOT method call delegation but insertion of customized functionalities on a specific method call.

<br /> class C</p> <p> def wish<br /> p “hello”<br /> end</p> <p> end</p> <p> c = C.new<br /> c.wish # hello</p> <p> class D</p> <p> class << self<br /> def keep_some_record<br /> p "I am keeping some records"<br /> end<br /> end</p> <p> end</p> <p> # aliasing the wish method</p> <p> c.class.module_eval do</p> <p> alias_method :wish_orig, :wish</p> <p> define_method :wish do<br /> D.keep_some_record<br /> wish_orig<br /> end</p> <p> end</p> <p> c.wish # I am keeping some records; hello<br />

4.) The Anonymous class

I just presented same a la this post

5.) send

Calling a method when method name is stored as a string object in a variable i.e. you can not see which method to call.
example 1
when method name is simply stored as a String object

<br /> class C<br /> def wish<br /> p “hello DELHI.rb”<br /> end<br /> end<br /> a = “wish”<br /> c = C.new<br /> c.send(a)<br />

example 2
making set method at runtime

<br /> class C<br /> attr_accessor :name<br /> end</p> <p> c = C.new</p> <p> a = “name”</p> <p> c.send(a + “=”, “SUR MAX”)</p> <p> p c.send(a)<br />

example 3
this is interesting, when attribute name itself is send

<br /> class C<br /> attr_accessor :send<br /> end</p> <p> c = C.new</p> <p> a = “send”</p> <p> c.__send__(a + “=”, “SUR MAX”)</p> <p> p c.__send__(a) # => Sur Max<br />

well, don’t say “what if attribute name is __send__”

6.) The Method class

Methods of the class are objects of the Method class when retrieved with the method method and can be called with the method call.
example 1
anything we define with def-end is an object of the class Method

<br /> class C<br /> def wish<br /> p “hello”<br /> end<br /> end</p> <p> c = C.new</p> <p> m1 = c.method(”wish”)</p> <p> p m1.class # => Method</p> <p> m1.call # => hello<br />

example 2
method can hold the object’s reference and associated instance variables

<br /> class C<br /> attr_accessor :name</p> <p> def initialize(name)<br /> self.name = name.to_s<br /> end</p> <p> def wish<br /> p “hello ” + name.to_s<br /> end<br /> end</p> <p> c = C.new(”Sur Max”)</p> <p> m1 = c.method(”wish”)<br /> m1.call # => hello Sur Max<br />

example 3
we are able to let this method object flow throughout the application code and let it available anywhere in the code.

<br /> class C<br /> attr_accessor :name</p> <p> def initialize(name)<br /> self.name = name.to_s<br /> end</p> <p> def wish<br /> p “hello ” + name.to_s<br /> end</p> <p> def self.supply_wish<br /> c = new(”Sur Max”)<br /> return c.method(”wish”)<br /> end</p> <p> end</p> <p> C.supply_wish.call # => hello Sur Max<br />

7.) what is “self”

I just presented a la this post

8.) Single Method Delegation – using Forwardable

Allows you to delegate named method calls to other objects.

<br /> require ‘forwardable’</p> <p> class C<br /> extend Forwardable</p> <p> attr_accessor :h</p> <p> def initialize<br /> @h = {}<br /> end</p> <p> def_delegator(:@h, :[], :show)<br /> def_delegator(:@h, :[]=, :add)</p> <p> end</p> <p> end</p> <p> c = C.new</p> <p> c.add(1, “asdf”)</p> <p> p c.show(1)</p> <p> p c.h<br />

Notice the beauty of ruby here… The methods [], []= of a hash object are usually called as

<br /> h = {}<br /> h["key"] # this will return the corresponding value<br /> h["key"] = “value” # this will set the “value” corresponding to the “key”<br />

BUT in the above delegation code we are calling them as(delegating the method call on them as)

<br /> h = {}<br /> h.[](”key”) # this will return the corresponding value<br /> h.[]=(”key”, “value”) # this will set the “value” corresponding to the “key”<br />

9.) Full class Delegation – using Delegator

Extending an object(instance of Class) with the capabilities of another.

<br /> require ‘delegate’</p> <p> class Words < DelegateClass(Array)</p> <p> def initialize(list = "one two three four")<br /> super(list.split)<br /> end</p> <p> end</p> <p> w = Words.new</p> <p> p w # => ["one", "two", "three", "four"]</p> <p> p w.length # => 4</p> <p>

10.) SimpleDelegator

Write memory optimized code with SimpleDelegator…

<br /> require ‘delegate’</p> <p> a = SimpleDelegator.new([10, 20])</p> <p> old_id = a.__id__</p> <p> b = a</p> <p> a.__setobj__(”a new object”) # this is not possible otherwise with the method “replace” which can replace only object of same class on same memory location</p> <p> new_id = a.__id__</p> <p> p a # => “a new object”<br /> p b # => “a new object”</p> <p> p new_id == old_id # => true<br />

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This entry was posted on Friday, July 20th, 2007 at 6:45 pm and is filed under RubyonRails, advance_ruby, classes, delegation, delhi.rb, duck typing, metaprogramming, rails, ror, ruby. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.