I uncover something new in Ruby nearly every day. Here’s a neat trick I learned today:

Suppose you have a User model, and that model has several methods that determine a user’s rights. Maybe something like User#can_delete?(object) and User#can_create_pages?.

Now suppose that in your view, you want to display a certain link only if a user is logged in AND if that user has rights to do that thing. So the delete link would look like this:

<%= link_to("delete", page_url(@page), :method => :delete) 
    if User.current_user and User.current_user.can_delete?(@page) %>

Yuk. Wordy. If you don’t check for User.current_user first, ActionView will raise an error because you’ll be requesting the can_delete? method from a nil object. So every time you want to display the delete link, you have to remember to process multiple conditions.

There is a better way.

In my ApplicationHelper, I defined a method called user?.

  def user?(*args, &block)
    return false unless User.current_user
    return true if args.first.blank?
    return User.current_user.send(*args, &block)
  end
  alias_method :user?, :user

Now we can rewrite that link code.

<%= link_to("delete", page_url(@page), :method => :delete) 
    if user(:can_delete?, @page) %>

Nice, eh?

We can do things like

user? #=> true | false
user(:can_create_pages?) #=> true | false
user(:can_edit?, @page) #=> true | false

The trick is in the *args variable. We pass the name of the method we’re calling as the first argument, and then any number of additional arguments, which will then be passed to the method specified in the first argument. Simple and clean.

[update] just fixed a couple of formatting issues.