Namespaces in Ruby

A namespace is a container for multiple items which includes classes, constants, other modules, and more. It is ensured in a namespace that all the objects have unique names for easy identification. Generally, they are structured in a hierarchical format so, that names can be reused. 

• Namespace in Ruby allows multiple structures to be written using hierarchical manner. Thus, one can reuse the names within the single main namespace.
• The namespace in Ruby is defined by prefixing the keyword module in front of the namespace name.
• The name of namespaces and classes always start from a capital letter.
• You can access the sub members of double with the help of :: operator. It is also called the constant resolution operator.
• Ruby allows nested namespace.
• You can use include keyword to copy the other module’s objects into the existing namespace without qualifying their name.

Syntax: 

module Namespace_name
    # modules.. and classes..
end

Example 1: 
This is an example of the simple formation of the namespace with a class and then executing the class methods defined within the class. Here, we access the sub members within the namespace, the “::” operator is used. It is also called the constant resolution operator. 

Ruby

# Ruby program to illustrate namespace

# Defining a namespace called Geek
module Geek
    class GeeksforGeeks

      # The variable gfg
        attr_reader :gfg

        # Class GeeksforGeeks constructor
        def initialize(value)
            @gfg = value
        end
    end
end

# Accessing the sub members of
# module using '::' operator
obj = Geek::GeeksforGeeks.new("GeeksForGeeks")
puts obj.gfg

Output:

GeeksForGeeks

Example 2:
This is an example showing the implementation of hierarchical namespacing. In this, there is a combination of class and namespace within the single namespace. Here, the use of the class name is done multiple times under the concept of hierarchical namespacing. 

Ruby

# Ruby program to illustrate namespace

# The main namespace
module Geek
    class GeeksforGeeks
        attr_reader :gfg
        def initialize(value)
            @gfg = value
        end
    end

    # Hierarchical namespace
    module Geek_1

      # Reuse of the class names
      class GeeksforGeeks
        @@var = "This is the module Geek_1 " +
                "and class GeeksforGeeks"
        def printVar()
            puts @@var
        end
      end
    end

    # Hierarchical namespace
    module Geek_2

      # Reuse of the class names
      class GeeksforGeeks
        attr_reader :var
        def initialize(var)
          @var = var
        end
      end
    end
  end

obj_gfg = Geek::GeeksforGeeks.new("This is the module Geek " +
                                  "and class GeeksforGeeks")
obj_gfg1 = Geek::Geek_1::GeeksforGeeks.new()
obj_gfg2 = Geek::Geek_2::GeeksforGeeks.new("This is the module Geek_2 " +
                                           "and class GeeksforGeeks")
puts obj_gfg.gfg
puts obj_gfg1.printVar()
puts obj_gfg2.var

Output:

This is the module Geek and class GeeksforGeeks
This is the module Geek_1 and class GeeksforGeeks

This is the module Geek_2 and class GeeksforGeeks