Why does Ruby have both private and protected methods?

by

protected methods can be called by any instance of the defining class or its subclasses.

private methods can be called only from within the calling object. You cannot access another instance’s private methods directly.

Here is a quick practical example:

def compare_to(x)
 self.some_method <=> x.some_method
end

some_method cannot be private here. It must be protected because you need it to support explicit receivers. Your typical internal helper methods can usually be private since they never need to be called like this.

It is important to note that this is different from the way Java or C++ works. private in Ruby is similar to protected in Java/C++ in that subclasses have access to the method. In Ruby, there is no way to restrict access to a method from its subclasses like you can with private in Java.

Visibility in Ruby is largely a “recommendation” anyways since you can always gain access to a method using send:

irb(main):001:0> class A
irb(main):002:1>   private
irb(main):003:1>   def not_so_private_method
irb(main):004:2>     puts "Hello World"
irb(main):005:2>   end
irb(main):006:1> end
=> nil

irb(main):007:0> foo = A.new
=> #<A:0x31688f>

irb(main):009:0> foo.send :not_so_private_method
Hello World
=> nil

More Related Contents:

  1. Why doesn’t Ruby support i++ or i–​ (increment/decrement operators)?
  2. Why does Ruby’s ‘gets’ includes the closing newline?
  3. Understanding private methods in Ruby
  4. How to create a private class method?
  5. Ruby syntax error, unexpected tIDENTIFIER, expecting end-of-input
  6. Ruby: String Comparison Issues
  7. Ruby 2.0.0p0 IRB warning: “DL is deprecated, please use Fiddle”
  8. Ruby metaclass confusion
  9. What are all the common ways to read a file in Ruby?
  10. What exactly is `&:capitalize` in Ruby?
  11. Difference between map and collect in Ruby?
  12. How do I get the match data for all occurrences of a Ruby regular expression in a string?
  13. What does __FILE__ mean in Ruby?
  14. Why isn’t the eigenclass equivalent to self.class, when it looks so similar?
  15. Ruby Hash with duplicate keys?
  16. Performance of Arrays and Hashes in Ruby
  17. Installing Jekyll without root
  18. gem eventmachine fatal error: ‘openssl/ssl.h’ file not found
  19. Is there an inverse ‘member?’ method in ruby?
  20. In Ruby, is there an Array method that combines ‘select’ and ‘map’?
  21. Running a command from Ruby displaying and capturing the output
  22. In Rails, how to add a new method to String class?
  23. Why isn’t self always needed in ruby / rails / activerecord?
  24. What does “
  25. Chrome 62 and Flash
  26. Ruby: Installing rmagick on Ubuntu
  27. Better ruby markdown interpreter?
  28. How to understand the difference between class_eval() and instance_eval()?
  29. What is the best way to split a string to get all the substrings by Ruby?
  30. Insert digital signature into existing pdf file

Leave a Comment