Introducing cache_annotations the other way round

In one of my last articles I introduced my lasted gem cache_annotations. Today I think it was explained as black vodoo, which might be uncomfortable to most readers. Therefore, I’ll start again, but the otherway round and everybody will love its simplicity.

cache_annotations

With CacheAnnotation you may easily provide your methods with an often needed caching. Suppose you are using the following piece of code:

class A
  def a
    @a ||= "some heavy computing that should be" +
        " done only once"
  end
end

This could look so much better:

class A
  include CacheAnnotation

  cached
  def a
    "some heavy computing that should be done only once"
  end
end

Or even better for single argumented methods:

class A
  def b(arg0)
    @b ||= {}
    @b[arg0] ||= "some heavy computing in " +
                 "respect to #{arg0} " +
                 "that should be done only once"
  end
end

vs.

class A
  include CacheAnnotation

  cached
  def b(arg0)
    "some heavy computing in respect to #{arg0} " +
    "that should be done only once"
  end
end

Behind the scenes, CacheAnnotation replaces the method body with the caching code. So the two versions are equal concerning behaviour and speed. If you don’t want CacheAnnotation to derive the instance variable’s name from the method name, you may supply a custom one:

class A
  include CacheAnnotation

  cached :in => :@b_cache
  def b(arg0)
    "some heavy computing in respect to #{arg0} " +
    "that should be done only once"
  end
end

If you want to use CacheAnnotation on the class side, you have to use a special technique to add these methods. It is described pretty good on http://www.dcmanges.com/blog/27

class A
  module ClassMethods
    include CacheAnnotation

    cached
    def c
      "some heavy computing that should " +
            "be done only once"
    end
  end
  self.extend(ClassMethods)
end

Final Remarks

That’s all the voodoo. Generating a simple method for you, basically the same thing attr_* does.

You will find other chunks of repeated code and you should think, if this could be stripped of and be used in a declarative way.