Support for a block observer in observer sets

Author: brainopia

lib/concurrent/atomic/copy_on_notify_observer_set.rb

@@ -15,12 +15,21 @@ def initialize
     # @param [Object] observer the observer to add
     # @param [Symbol] func the function to call on the observer during notification. Default is :update
     # @return [Symbol] the added function
-    def add_observer(observer, func=:update)
+    def add_observer(observer=nil, func=:update, &block)
+      unless !!observer ^ block # xor
+        raise ArgumentError, 'should pass observer as a first argument or block'
+      end
+
+      if block
+        observer = block
+        func = :call
+      end
+
       @mutex.lock
       @observers[observer] = func
       @mutex.unlock
 
-      func
+      observer
     end
 
     # @param [Object] observer the observer to remove

lib/concurrent/atomic/copy_on_write_observer_set.rb

@@ -14,14 +14,23 @@ def initialize
     # @param [Object] observer the observer to add
     # @param [Symbol] func the function to call on the observer during notification. Default is :update
     # @return [Symbol] the added function
-    def add_observer(observer, func=:update)
+    def add_observer(observer=nil, func=:update, &block)
+      unless !!observer ^ block # xor
+        raise ArgumentError, 'should pass observer as a first argument or block'
+      end
+
+      if block
+        observer = block
+        func = :call
+      end
+
       @mutex.lock
       new_observers = @observers.dup
       new_observers[observer] = func
       @observers = new_observers
       @mutex.unlock
 
-      func
+      observer
     end
 
     # @param [Object] observer the observer to remove

spec/concurrent/atomic/observer_set_shared.rb

@@ -8,15 +8,16 @@
 
   describe '#add_observer' do
 
-    context 'with argument' do
-      it 'should return the passed function' do
-        observer_set.add_observer(observer, :a_method).should eq(:a_method)
+    context 'with arguments' do
+      it 'should return the observer' do
+        observer_set.add_observer(observer, :a_method).should == observer
       end
     end
 
-    context 'without arguments' do
-      it 'should return the default function' do
-        observer_set.add_observer(observer).should eq(:update)
+    context 'with a block' do
+      it 'should return the observer based on a block' do
+        observer = observer_set.add_observer { :block }
+        observer.call.should == :block
       end
     end
   end
@@ -61,6 +62,14 @@
         observer_set.notify_observers('a string arg')
       end
 
+      it 'should notify an observer from a block' do
+        notification = double
+        expect(notification).to receive(:catch)
+
+        observer_set.add_observer {|arg| arg.catch }
+        observer_set.notify_observers notification
+      end
+
       it 'can be called many times' do
         expect(observer).to receive(:update).with(:an_arg).twice
         expect(observer).to receive(:update).with(no_args).once