how to dynamicaly call a method while repecting privacy

Question

Using dynamic method calls (#send or #method) the methods visibility is ignored.
is there a simple way to dynamically call a method that will fail calling a private method?

Answer 1

Thought I don't understand why you want to do so, you can use eval.

class Klass
  private
    def private_method(arg)
    end
end

k = Klass.new
m = "private_method"
eval "k.#{m}('an arg')"

NoMethodError: private method `private_method' called for #<Klass:0x128a7c0>
    from (irb):15
    from (irb):15

Answer 2

If you are using ruby-1.9, you can use Object#public_send which does what you want.

If you use ruby-1.8.7 or earlier you have to write your own Object#public_send

class Object
  def public_send(name, *args)
    unless public_methods.include?(name.to_s)
      raise NoMethodError.new("undefined method `#{name}' for \"#{self.inspect}\":#{self.class}")
    end
    send(name, *args)
  end
end

Or you could write your own Object#public_method which behaves like Object#method but only for public methods

class Object
  def public_method(name)
    unless public_methods.include?(name.to_s)
      raise NameError.new("undefined method `#{name}' for class `#{self.class}'")
    end
    method(name)
  end
end

Answer 3

As I know - you need method public_send:

----------------------------------------------------- Object#public_send
     obj.public_send(symbol [, args...])  => obj

     From Ruby 1.9.1
------------------------------------------------------------------------
     Invokes the method identified by _symbol_, passing it any arguments
     specified. Unlike send, public_send calls public methods only.

        1.public_send(:puts, "hello")  # causes NoMethodError

Answer 4

It's true though, eval really is I think the only way to actually do it pre-1.9. If you want to read more about visibility Jamis Buck wrote an awesome article about what method visibility actually means in Ruby.

Much like other things in Ruby visibility is ever so slightly different than other languages.

Answer 5

require 'backports'  # Needed for Ruby < 1.9

my_object.public_send :method, *args

My backports gem defines all of Ruby 1.8.7 and many Ruby 1.9 methods, including public_send, which is what you want to use here.