Understand Ruby Visibility

A part of Ruby that has come back to bite many developers (and even worse those that are not writing tests (for shame)) is its handling of visibility- public, protected and private. So I wanted to break it down a bit with a concrete example (Ruby 2.1.2)-

 class Person

 def apublic
 puts "I am public"
 end

 def instance_check_protected(i)
 i.aprotected
 end

 def instance_check_private(i)
 i.aprivate
 end

 def call_protected_self
 self.aprotected
 end

 def implicit_protected
 aprotected
 end

 def call_private_self
 self.aprivate
 end

 def implicit_private
 aprivate
 end

 protected def aprotected
 puts "I am protected"
 end

 private def aprivate
 puts "I am private"
 end

end

Now our class is all set up, let's try it out.

p = Person.new

p.apublic # I am public
p.aprotected # protected method `aprotected' called for #<Person:0x007ffafaa175f0> (NoMethodError)
p.aprivate # private method `aprivate' called for #<Person:0x007fec208ef670> (NoMethodError)

p.send(:aprotected) # I am protected
p.method(:aprotected).call # I am protected

p.send(:aprivate) # I am private
p.method(:aprivate).call # I am private

p.call_protected_self # I am protected
p.implicit_protected # I am protected

p.instance_check_protected(Person.new) # I am protected
p.instance_check_private(Person.new) # private method `aprivate' called for #<Person:0x007fbf98a2f2d8> (NoMethodError)

p.call_private_self # private method `aprivate' called for #<Person:0x007f8d6a8976b0> (NoMethodError)
p.implicit_private # I am private