When, a Rails plugin

Ever write this?

before_filter :authorize

protected

def authorize
  unless logged_in?
    session[:return_to] = request.request_uri
    redirect_to login_url and return false
  end
end

You want your before_filter to authorize the current_user unless they are logged in. So why not say it like you mean it?

before_filter :authorize, :unless => logged_in?

protected

def authorize
  session[:return_to] = request.request_uri
  redirect_to login_url and return false
end

This is more expressive. The conditional logic is no longer hidden in the method.

The authorize method now has a single responsibility: to authorize. The before_filter, responsible for performing some action before your controller action is called, is now smarter about when it is supposed to run.

Introducing When

The When Rails plugin adds :if and :unless modifiers to before_filters, most ActiveRecord callbacks, and validations.

Use it to improve your controllers:

before_filter :deny_access, :unless => :admin?

protected

def deny_access
  flash[:failure] = "You do not have access to that page."
  redirect_to home_url
end

def admin?
  logged_in? and current_user.admin?
end

Improve your models, too:

before_create :encrypt_password,
  :unless => lambda {|user| user.password_confirmation.blank?}

after_save :send_alerts, :if => :alerts?

validate_on_create :add_unsupported_type_error,
  :unless => lambda {|document| SUPPORTED_FILE_TYPES.include? document.file_type}

Coding Without Ifs

Jared makes a strong argument that this is actually removing conditional logic from your program. I tend to agree.

It reminds me of defining constants in your environments so you don’t write conditional logic that checks the RAILS_ENV. That kind of control flow belongs in the framework.

Whether this is removing conditional logic is moot, though. It just feels right, and isn’t that why we write Ruby?

Update: after releasing this, we found out this is already in Rails trunk. Awesome! It’s a great feature and should be in the framework. So, if you’re not running on Edge, use the when plugin to get this feature now. Then, remove it when you upgrade to the next version of Rails, when you’ll get :ifs and :unlesses for free. Happy coding!