Ruby - 2. Class and Instance Variables II 2020

Ruby provides four variable types:

1. Local Variables: Local variables are the variables that are defined in a method. Local variables are not available outside the method. Local variables begin with a lowercase letter or _.
2. Instance Variables: Instance variables are available across methods for any particular instance or object. That means that instance variables change from object to object. Instance variables are preceded by the at sign (@) followed by the variable name.
3. Class Variables: Class variables are available across different objects. A class variable belongs to the class and is a characteristic of a class. They are preceded by the sign @@ and are followed by the variable name.
4. Global Variables: Class variables are not available across classes. So, if we want to have a single variable, which is available across classes, we need to define a global variable. The global variables are always preceded by the dollar sign ($).

Using the class variable @@no_of_objs, we can determine the number of objects that are being created. This enables in deriving the number of users.

class User
   @@no_of_users=0
end

class User
   @@no_of_usmers=0
   def initialize(id, name)
      @user_id=id
      @user_name=name
   end
end

We declared the initialize method with id and name as local variables. Here, def and end are used to define a Ruby method initialize.

In the initialize method, we pass these local variables to the instance variables @user_id and @user_name where local variables hold the values that are passed along with the new method.

They are special variables that have the appearance of local variables but behave like constants. We can not assign any value to these variables.:

1. self: The receiver object of the current method.
2. true: Value representing true.
3. false: Value representing false.
4. nil: Value representing undefined.
5. __FILE__: The name of the current source file.
6. __LINE__: The current line number in the source file.

Ruby on Rails

• Ruby On Rails Home
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• Ruby - Class and Instance Variables II
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• Deploying a Rails 4 app on CentOS 7 production server with Apache and Passenger I
• Deploying a Rails 4 app on CentOS 7 production server with Apache and Passenger II
• OOPS! Deploying a Rails 4 app on CentOS 7 production server with Apache and Passenger (Trouble shooting)