adding 'cannot?' method which performs opposite check of 'can?' - closes #1

CHANGELOG.rdoc

@@ -1,3 +1,5 @@
+* adding "cannot?" method to ability, controller, and view which is inverse of "can?" - see issue #1
+
 * BACKWARDS INCOMPATIBLE: use Ability#initialize instead of 'prepare' to set up abilities - see issue #4
 
 *0.1.0* (Nov 16th, 2009)

README.rdoc

@@ -38,17 +38,17 @@ First define a class called Ability, place it in "models/ability.rb".
 
 This class is where all permissions will go. See the "Defining Abilities" section below for more information.
 
-In the view layer you can access the current permissions at any point using the "can?" method. See "Checking Abilities" section below.
+In the view layer you can access the current permissions at any point using the "can?" and "cannot?" methods. See "Checking Abilities" section below.
 
   <% if can? :update, @article %>
     <%= link_to "Edit", edit_article_path(@article) %>
   <% end %>
 
-You can also use this method in the controller layer along with the "unauthorized!" method to restrict access.
+You can also use these methods in the controller layer along with the "unauthorized!" method to restrict access.
 
   def show
     @article = Article.find(params[:id])
-    unauthorized! unless can? :read, @article
+    unauthorized! if cannot? :read, @article
   end
 
 Setting this for every action can be tedious, therefore a before filter is also provided for automatically applying this setting to a RESTful style resource controller.
@@ -135,6 +135,10 @@ You can also pass the class instead of an instance (if you don't have one handy)
     <%= link_to "New Project", new_project_path %>
   <% end %>
 
+The "cannot?" method is for convenience and performs the opposite check of "can?"
+
+  cannot? :destroy, @project
+
 
 == Custom Actions
 
@@ -148,7 +152,7 @@ There is no limit to what actions you can use to determine abilities. For exampl
   
   # projects_controller.rb
   def update
-    unauthorized! if params[:project][:upload_picture] && !can?(:upload_picture, @project)
+    unauthorized! if params[:project][:upload_picture] && cannot?(:upload_picture, @project)
     # ...
   end
 
@@ -199,7 +203,7 @@ def test "user can only destroy projects which he owns"
   user = User.new
   ability = Ability.new(user)
   assert ability.can?(:destroy, Project.new(:user => user))
-  assert !ability.can?(:destroy, Project.new)
+  assert ability.cannot?(:destroy, Project.new)
 end
 
 

lib/cancan/ability.rb

@@ -21,6 +21,10 @@ module CanCan
       false
     end
     
+    def cannot?(*args)
+      !can?(*args)
+    end
+    
     def possible_actions_for(initial_action)
       actions = [initial_action]
       (@aliased_actions || default_alias_actions).each do |target, aliases|

lib/cancan/controller_additions.rb

@@ -1,7 +1,7 @@
 module CanCan
   module ControllerAdditions
     def self.included(base)
-      base.helper_method :can?
+      base.helper_method :can?, :cannot?
     end
     
     def unauthorized!
@@ -16,6 +16,10 @@ module CanCan
       (@current_ability ||= current_ability).can?(*args)
     end
     
+    def cannot?(*args)
+      (@current_ability ||= current_ability).cannot?(*args)
+    end
+    
     def load_resource # TODO this could use some refactoring
       unless params[:action] == "index"
         if params[:id]

spec/cancan/ability_spec.rb

@@ -81,4 +81,8 @@ describe CanCan::Ability do
   it "should not respond to prepare (now using initialize)" do
     @ability.should_not respond_to(:prepare)
   end
+  
+  it "should offer cannot? method which is simply invert of can?" do
+    @ability.cannot?(:tie, String).should be_true
+  end
 end

spec/cancan/controller_additions_spec.rb

@@ -11,7 +11,7 @@ describe CanCan::ControllerAdditions do
   before(:each) do
     @controller_class = Class.new
     @controller = @controller_class.new
-    mock(@controller_class).helper_method(:can?)
+    mock(@controller_class).helper_method(:can?, :cannot?)
     @controller_class.send(:include, CanCan::ControllerAdditions)
   end
   
@@ -26,10 +26,11 @@ describe CanCan::ControllerAdditions do
     @controller.current_ability.should be_kind_of(Ability)
   end
   
-  it "should provide a can? method which goes through the current ability" do
+  it "should provide a can? and cannot? methods which go through the current ability" do
     stub(@controller).current_user { :current_user }
     @controller.current_ability.should be_kind_of(Ability)
     @controller.can?(:foo, :bar).should be_false
+    @controller.cannot?(:foo, :bar).should be_true
   end
   
   it "should load the resource if params[:id] is specified" do