ruby - Cast between String and Classname

Question

I have a string, containing an Class name. It is, for example, a string containing "Article". That string came up from the params[]. What should I do to work with this string as if it was a class name? For instance, I want to do:

Article.all

and so on.

Any idea?

Answer 1

This solution is better than eval as you are evaluating params hash that might be manipulated by the user and could contain harmful actions. As a general rule: Never evaluate user input directly, that's a big security hole.

# Monkey patch for String class
    class String
      def to_class
        klass = Kernel.const_get(self)
        klass.is_a?(Class) ? klass : nil
      rescue NameError
        nil
      end
    end

# Examples
"Fixnum".to_class #=> Fixnum
"Something".to_class #=> nil

Update - a better version that works with namespaces:

 # Monkey patch for String class
    class String
      def to_class
        chain = self.split "::"
        klass = Kernel
        chain.each do |klass_string|
          klass = klass.const_get klass_string
        end
        klass.is_a?(Class) ? klass : nil
      rescue NameError
        nil
      end
    end