use Perl

• Pimping Ruby (Score:2)

  by djberg96 (2603) on 2006.12.10 10:44 (#52176) Journal

  I 've been trying to maintain some legacy code that badly needs updating. One of the main sins committed in this code is direct object access, so $obj->{attribute} = 'value', rather than $obj->set_attribute('value');

  This is one of those areas where Ruby's Uniform Access Principle demonstrates just how clunky Perl's OO and accessors really are. To wit:

  class Foo
     attr_accessor :attribute
  end
  
  obj = Foo.new
  obj.attribute = 'value'

  "But, wait!", you cry. "Accessing the attribute like that is an encapsulation violation!"

  You're not accessing the attribute directly. The syntax just makes it *look* like you are. In reality you're calling the Foo#attribute= method. This longhand example should clarify things:

     class Foo
        attr_reader :attribute
        def initialize
           @attribute = 7
        end
        def attribute=(value)
           puts "Hello World!"
        end
     end
  
     obj = Foo.new
     puts obj.attribute # 7
     obj.attribute = 99 # "Hello World!"
     puts obj.attribute # 7 - wasn't touched

  Reply to This

  • Re: (Score:1)

    by chromatic (983)

    def initialize
        @attribute = 7
    end

    This is one of those areas where Perl 6's Uniform Access Principle demonstrates just how clunky and non-uniform Ruby's instance attributes are.
    • Re: (Score:2)

      by djberg96 (2603)

      I assume you mean the fact that Perl 6 provides default read-only (though configurable) accessors on attributes. That's what I get from Exegesis 12, anyway, unless something has changed.

      Personally, I think it's a misfeature, because I don't always want users to have access to the instance variables I'm using. I'm sure that's configurable, too, but I'd rather be explicit than implicit in this case. Or, just write a custom 'is' method that lets me imitate the Perl 6 syntax.

      The topic of autogenerating a
      • Re: (Score:1)

        by chromatic (983)

        I actually meant that most of the Ruby code I've seen accesses instance variables directly within the class, despite the presence of an autogenerated accessor. There's a subclassing problem there. (Actually it's not only a problem for subclassing, but I use that as a convenient shorthand because I don't have a good way to say "allomorphic instance modification".)

        The fact that there has never been a clamoring for it among the Ruby community ought to be telling, though.

        I've never seen a clamoring for
        • Re: (Score:2)

          by djberg96 (2603)

          I actually meant that most of the Ruby code I've seen accesses instance variables directly within the class, despite the presence of an autogenerated accessor. There's a subclassing problem there.

          I'm afraid I don't follow. Unless you have a custom writer, doing "self.attribute = 'value'" instead of "@attribute = 'value'" is a wasted method lookup. I fail to see what subclassing problem you would have.

          I've never seen a clamoring for a saner require either, but I don't take that as evidence that it's a particularly clear, clean, or well-defined feature.

          My only gripe with require is that it doesn't look in its own directory first, and so all the library authors end up doing $LOAD_PATH.unshift(File.dirname(__FILE__)) in each file. Otherwise, I'm not sure what you're referring to.
          • Re: (Score:1)

            by chromatic (983)

            I fail to see what subclassing problem you would have.

            It's only a problem if a subclass wants to do something different with an attribute. I run into that once in a while.
            • Re: (Score:2)

              by djberg96 (2603)

              Can you provide an example that demonstrates the issue?