Whats there in an Object
Lets start with the basics and look at the following piece of Ruby code:
class A def method @v = 1 end end a = A.new a.class # => A
1) Instance Variables:
Objects contain instance variables, Ruby provides a method Object#instance_variables() to peek at them.
In the above example we have just one instance variable
a.method a.instance_variables # => [:@v]
Unlike in static languages like Java, in Ruby there is no connection between an object's class and its instance variables.
Instance Variables come into existence whenever you assign them a value. Important thing to understand is that you can have objects of the "same" class that carry different sets of instance variables
Lets look at the following example:
class A def method @v = 1 end def new_method @c = 2 end end a = A.new a.method a.instance_variables #=> [:@v] b = A.new b.new_method b.instance_variables #=> [:@c]
So if we hadn't called a.method() or b.new_method() objects a or b would not have any instance variables.
Besides having instance variables objects have methods
You can see an objects methods by calling Object#methods(). Most of the methods will be the methods inherited from Object so this list of methods will be quite long.
We can use Array#grep() to find the method we are looking for
a.methods.grep(/new_/) #=> [:new_method]
3) Classes: Yes, classes are nothing but objects in ruby and since a class is an object, everything that applies to an object also applies to a class.
Classes like any object have their own class, called Class
"hello".class # => String
The method of an object are the instance methods of its class.
Methods of a class are the instance methods methods of Class.