Open-Close Principle

open-close.rb

# This is a bad solution that violates open-closed principle
class Document
  def initialize(path, doc_type)
    @path = path
    @doc_type = doc_type
  end

  def parse
    case doc_type
    when :docx
      # some docx parsing functionality
    when :pdf
      # some pdf parsing functionality
    end
  end
end

# A good example where all extensions are made according to the open/closed principle

class Document
  def initialize(path, parser_class)
    @path = path
    @parser_service = parser_class.new(@path)
  end

  def parse
    parser_service.parse
  end
end

class BaseDocumentParser
  def initialize(path)
    @path = path
  end
end

class PdfDocumentParser < BaseDocumentParser
  def parse
    p 'some pdf parsing functionality'
  end
end

class DocxDocumentParser < BaseDocumentParser
  def parse
    p 'some docx parsing functionality'
  end
end

#we can now extend our Document class functionality without modifying it. 
#When we need to add a new document type, we will not have to modify the Document class.
Document('paths', PdfDocumentParser).parse