Classes in Ruby

In programming, security and reusability are the big challenges in programming. The classes help to resolve these challenges. The classes are the collection of the statements (code). Classes can be called from outside, so we can use code inside the class again and again. The classes can define who can access its code. It helps in restricting unwanted people to access important code.

The simple syntax of the class is:

#define class with keyword 'class'
class ClassName
  #code of the class
end
#close class with keyword 'end'

Class name can be anything including only alphabets, numbers and underscore. For good coding practice start class name with capital letter.

Objects

The code of the class can not be executed directly. We need to make some reference to that class. This reference is called object. We call (execute) a class by using this object.

#define class with keyword 'class'
class ClassName2
  #code of the class
end
#close class with keyword 'end'

# making the object of above class
# the rules for the name of the object 
# are same as that for variable name
object = ClassName2.new

Methods inside class:

Methods can be inside the class.

# methods with classes
class MyClass
  # methods inside the class
  def print_name(name, age)
    puts "your name is #{name} and age is #{age}"
  end
end

o = MyClass.new
# calling the method
o.print_name 'ha', 2

Class methods:

The class methods are special methods which are independent of objects and only depend on the class. These are equivalent to static methods/ functions in other programming languages.

# methods with classes
class MyClass
  # methods inside the class
  def print_name(name, age)
    puts "your name is #{name} and age is #{age}"
  end
  
  # defining a class method
  def MyClass.static
    puts 'this is static method'
  end
end

o = MyClass.new
# calling the method
o.print_name 'ha', 2

# calling static method
MyClass.static

Output:

your name is ha and age is 2
this is static method

NOTE:

The variables which are defined in general methods are not available inside the class methods.
The class methods can not be called directly even inside the same class. These methods can only be called using class name. Class method can be called directly in other class methods.
General methods also can not be called directly in the class methods. For calling general methods, class object must be created in class methods.
We can also use keyword self instead of class name to define a class method.

Constructor:

It is special type of the method which runs automatically when we make the object of the class. This method is used to initialize variables within a class.

class MyClass
  def initialize
    puts 'this is a constructor and is used to initialize the variables'
  end
end

o = MyClass.new

Output:

this is a constructor and is used to initialize the variables

Class variables:

Class variables are accessible only in the class. All objects of the same class share class variables.

class ClassName
  def initialize
    @@class_variable = 12
    @instance_variable = 12
  end
  
  def get_cls_var
    @@class_variable+=1
    return @@class_variable
  end
  
  def get_ins_var
    @instance_variable+=1
    return @instance_variable
  end
end

obj1 = ClassName.new
obj2 = ClassName.new

puts obj1.get_ins_var
puts obj2.get_ins_var
puts obj1.get_ins_var
puts obj2.get_ins_var

# operating class varaible
puts obj1.get_cls_var
puts obj2.get_cls_var
puts obj1.get_cls_var
puts obj2.get_cls_var

Output:

Note that both object have different instance variables but both objects are operating on same class variable.

Object properties:

Methods can be defined from outside the class.

class MyClass
  
end

o = MyClass.new

# defining a object property
def o.method
  puts 'this is general method from outside'
end

#defining class method
def MyClass.cls_method
  puts 'this is class method'
end

# calling methods
o.method
MyClass.cls_method

Output:

this is general method from outside
this is class method

Modifiers:

In the staring of this article we had discussed that classes help in security. We can restrict the accessibility of methods and objects. Ruby defines three access controls:

public: Accessible to anybody
private: Only accessible within the class
protected: Can be invoked only by objects of the defining class and its subclasses. We will read about it in inheritance.

class MyClass
 
# public methods
public
def for_all
  puts 'this is for all'
end  

# place more public methods here

# private methods
private
def secret
  puts 'this is secret method'
end

# write more private methods here

#protected
protected
def family
  puts 'this is inheritable method, not for all'
end

# place more protected methods here
end

o = MyClass.new
o.for_all
# can not call other two
# o.secret
# o.family

Classes in Ruby

Objects

Methods inside class:

Class methods:

NOTE:

Constructor:

Class variables:

Object properties:

Modifiers:

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