yamori yamori - 5 months ago 22
Ruby Question

Ruby class with static method calling a private method?

I have a class with a number of static methods. Each one has to call a common method, but I'm trying not to expose this latter method. Making it private would only allow access from an own instance of the class? Protected does not seem like it would solve the problem here either.

How do I hide do_calc from being called externally in a static context? (Leaving it available to be called from the first two static methods.)

class Foo
def self.bar
do_calc()
end
def self.baz
do_calc()
end
def self.do_calc
end
end

Answer

First off, static is not really part of the Ruby lingo.

def self.foo
end

defines the method foo on an explicit object, in this case the containing class. Yes, it can be defined a class method, but static does not really make sense in Ruby.

Then private would not work, because defining a method on an explicit object (e.g. def self.foo) bypasses the access qualifiers and makes the method public.

What you can do, is to use the class << self syntax to open the metaclass of the containing class, and define the methods there as instance methods:

class Foo
  class << self

    def bar
      do_calc
    end

    def baz
      do_calc
    end

    private

    def do_calc
      puts "calculating..."
    end
  end
end

This will give you what you need:

Foo.bar
calculating...

Foo.baz
calculating...

Foo.do_calc
NoMethodError: private method `do_calc' called for Foo:Class