Ruby annotations
In the programming world, an annotation is a way to mark the code that is below it for many purposes. In Cucumber, the tags it uses are a kind of annotation to apply callbacks and classify some features and scenarios:
@billing Feature: Verify billing @important Scenario: Missing product description Scenario: Several products
In the case of VRaptor, we can use annotations to specify a controller as a REST resource or to restrict the access method to an action:
@Resource public class ShoppingCartController { ... } public class ProductsController { @Post @Path("/products") public void add(Product product) {...} ... }
In the Ruby language, two annotations that are very used are the methods protected and private, which without arguments restrict the visibility of the methods defined below them:
class User def jump; end; protected def eat; end; def flirt; end; private def sleep; end; def dream; end; end
In some situations we may want to annotate our code like this, for example to specify that a method is deprecated, functionality that is offered by the gem Canivete from Douglas Campos:
class Bomb deprecate def explode; end end
In the previous code, when somebody calls Bomp#explode, the interpreter will effectively execute the method, but also will output: Warning: calling deprecated method Bomb.explode.
The key to this behavior is the method_added method which is present in all Ruby modules and which is called every time a method is defined, receiving the name of the method as the parameter.
We can use this method, for example, to create an annotation that specifies that the methods declared below it can only be called by an admin, something like this:
class Module def method_added(name) unless @_admin_only.nil? or @_proxy_method @_proxy_method = true alias_method "_admin_#{name}", name module_eval <<-STRING def #{name}(*args, &block) _admin_#{name}(*args, &block) if admin? end STRING @_proxy_method = false end end def admin_only @_admin_only = true end end class User def admin? [true, false][rand(2)] end admin_only def update_password puts "password updated" end def restart_server puts "server restarted" end end
In the previous code, #admin? will randonmly return true or false and depending of the result the called method will be executed or not.
Bookmarked under ‘cool ruby code’, I’ve been doing Ruby over 6 years now and I’m always learning new techniques.
An interesting point is that the private and protected methods can also take a block, and it would be simple to add that functionality to your helper like so:
you might also want to override the private and protected methods to set @_admin_only to false again, so that they can work better
Lenary
Nice article
Does @_admin_only is a class instance variable?
Great article. Just started with Ruby (and Rails) a few months ago from the Java world and meta-programming is the key to the castle.
@Lenary
Yes, you’re right, that would be cool.
@slawosz
Yes, I like to named it with ‘_’ to be kind of ‘private’
Thanks for the feedback.
Youre so awesome, man! I cant believe I missed this blog for so long. Its just great stuff all round. Your design, man…too amazing! I cant wait to read what youve got next. I love everything that youre saying and want more, more, MORE! Keep this up, man! Its just too good.:)
Seriosly, I’m a blog fan and with all of the blogs out there now, not all of them that has been posted stands out like yours does. Your blog caught my eye and I really like your ideas that you’ve benn shared with us..Thumbs up!
Great post. One sugestion: I think .method_added(name) would be better moved to a module e.g. AdminOnly and super should be added into .method_added(name) somewhere. Then class User can be extended with AdminOnly without overhead (from extending Module directly) and without breaking any other magic already using .method_added.
module AdminOnly
def method_added(name)
# …
super
end
def admin_only
@_admin_only = true
end
end
class User
extend AdminOnly
# …
end
Thanks for your recommendations on this blog. One particular thing I would choose to say is always that purchasing gadgets items in the Internet is nothing new. The fact is, in the past several years alone, the market for online electronic products has grown noticeably. Today, you will find practically just about any electronic system and gizmo on the Internet, including cameras as well as camcorders to computer parts and games consoles.
Wonderful work! This is the kind of info that are meant to be shared across the net. Shame on search engines for now not positioning this submit higher! Come on over and discuss with my web site . Thanks =)
Wonderful items of your stuff, man. I’ve comprehend your own stuff before and you are too excellent. I like what you have acquired right here, definitely like what youíre stating and exactly how in which you say it. You make this enjoyable but you just take care of to keep this wise. We canít wait to read a lot more from you. This is really a terrific web site.I truly wanted to make a small remark to be able to convey appreciation for you for all the fantastic info you are discussing only at that website. Time intensive web research has at the conclusion been rewarded along with wonderful understanding to write about along with my friends. I’d point out that most of us readers are unequivocally rendered to stay in an excellent location along with lots of marvellous people with useful techniques. Personally i think truly fortunate to possess come across your entire web page and look toward really more enjoyable times reading through here. Thanks once again with regard to everything.
I’ve observed that in the world the present moment, video games are the latest rage with children of all ages. There are times when it may be difficult to drag your children away from the activities. If you want the best of both worlds, there are several educational games for kids. Great post.
The best website…
[...]For your wins to be made.it is to be noted that there are number of[...]…