private                 → self
private(symbol, ...)    → self

With no arguments, sets the default visibility for subsequently defined methods to private. With arguments, sets the named methods to have private visibility.

module Mod
  def a()  end
  def b()  end
  private
  def c()  end
  private :a
end
Mod.private_instance_methods   #=> ["a", "c"]

Source Code

/*
*  call-seq:
*     private                 => self
*     private(symbol, ...)    => self
*  
*  With no arguments, sets the default visibility for subsequently
*  defined methods to private. With arguments, sets the named methods
*  to have private visibility.
*     
*     module Mod
*       def a()  end
*       def b()  end
*       private
*       def c()  end
*       private :a
*     end
*     Mod.private_instance_methods   #=> ["a", "c"]
*/

static VALUE
rb_mod_private(argc, argv, module)
   int argc;
   VALUE *argv;
   VALUE module;
{
   secure_visibility(module);
   if (argc == 0) {
       SCOPE_SET(SCOPE_PRIVATE);
   }
   else {
       set_method_visibility(module, argc, argv, NOEX_PRIVATE);
   }
   return module;
}