instanceof.diff

--- a/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
+++ b/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
@@ -157,6 +157,16 @@ class YamlFileLoader extends FileLoader
         if (!is_array($content['services'])) {
             throw new InvalidArgumentException(sprintf('The "services" key should contain an array in %s. Check your YAML syntax.', $file));
         }
+
+        if (isset($content['services']['_instanceof'])) {
+            if (!is_array($types = $content['services']['_instanceof'])) {
+                throw new InvalidArgumentException(sprintf('The "_instanceof" key must contain an array, "%s" given in "%s".', gettype($types), $file));
+            }
+            foreach ($types as $id => $service) {
+                $this->parseDefinition($id, $service, $file, array(), true);
+            }
+        }
+
         if (isset($content['services']['_defaults'])) {
             if (!is_array($defaults = $content['services']['_defaults'])) {
                 throw new InvalidArgumentException(sprintf('Service defaults must be an array, "%s" given in "%s".', gettype($defaults), $file));
@@ -206,7 +216,7 @@ class YamlFileLoader extends FileLoader
         }
 
         foreach ($content['services'] as $id => $service) {
-            $this->parseDefinition($id, $service, $file, $defaults);
+            $this->parseDefinition($id, $service, $file, $defaults, false);
         }
     }
 
@@ -217,10 +227,11 @@ class YamlFileLoader extends FileLoader
      * @param array  $service
      * @param string $file
      * @param array  $defaults
+     * @param bool   $isConditionalType
      *
      * @throws InvalidArgumentException When tags are invalid
      */
-    private function parseDefinition($id, $service, $file, array $defaults)
+    private function parseDefinition($id, $service, $file, array $defaults, $isConditionalType)
     {
         if (is_string($service) && 0 === strpos($service, '@')) {
             $public = isset($defaults['public']) ? $defaults['public'] : true;
@@ -410,7 +421,7 @@ class YamlFileLoader extends FileLoader
             }
         }
 
-        $this->container->setDefinition($id, $definition);
+        $this->setDefinition($id, $definition, $isConditionalType);
     }
 
     /**

loader.diff

diff --git a/src/Symfony/Component/DependencyInjection/Loader/FileLoader.php b/src/Symfony/Component/DependencyInjection/Loader/FileLoader.php
index 90cd6bc..4171d8b 100644
--- a/src/Symfony/Component/DependencyInjection/Loader/FileLoader.php
+++ b/src/Symfony/Component/DependencyInjection/Loader/FileLoader.php
@@ -24,6 +24,8 @@ abstract class FileLoader extends BaseFileLoader
 {
     protected $container;
 
+    private $conditionalTypes = array();
+
     /**
      * @param ContainerBuilder     $container A ContainerBuilder instance
      * @param FileLocatorInterface $locator   A FileLocator instance
@@ -34,4 +36,15 @@ abstract class FileLoader extends BaseFileLoader
 
         parent::__construct($locator);
     }
+
+    public function setDefinition($id, Definition $definition, $isConditionalType = false)
+    {
+        if ($isConditionalType) {
+            $this->conditionalTypes[$id] = $definition;
+
+            return;
+        }
+
+        $this->container->setDefinition($id, $definition);
+    }
 }
diff --git a/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php b/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
index 1329d22..3fe8ad6 100644
--- a/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
+++ b/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
@@ -157,6 +157,16 @@ class YamlFileLoader extends FileLoader
         if (!is_array($content['services'])) {
             throw new InvalidArgumentException(sprintf('The "services" key should contain an array in %s. Check your YAML syntax.', $file));
         }
+
+        if (isset($content['services']['_instanceof'])) {
+            if (!is_array($types = $content['services']['_instanceof'])) {
+                throw new InvalidArgumentException(sprintf('The "_instanceof" key must contain an array, "%s" given in "%s".', gettype($types), $file));
+            }
+            foreach ($types as $id => $service) {
+                $this->parseDefinition($id, $service, $file, array(), true);
+            }
+        }
+
         if (isset($content['services']['_defaults'])) {
             if (!is_array($defaults = $content['services']['_defaults'])) {
                 throw new InvalidArgumentException(sprintf('Service defaults must be an array, "%s" given in "%s".', gettype($defaults), $file));
@@ -206,7 +216,7 @@ class YamlFileLoader extends FileLoader
         }
 
         foreach ($content['services'] as $id => $service) {
-            $this->parseDefinition($id, $service, $file, $defaults);
+            $this->parseDefinition($id, $service, $file, $defaults, false);
         }
     }
 
@@ -217,10 +227,11 @@ class YamlFileLoader extends FileLoader
      * @param array  $service
      * @param string $file
      * @param array  $defaults
+     * @param bool   $isConditionalType
      *
      * @throws InvalidArgumentException When tags are invalid
      */
-    private function parseDefinition($id, $service, $file, array $defaults)
+    private function parseDefinition($id, $service, $file, array $defaults, $isConditionalType)
     {
         if (is_string($service) && 0 === strpos($service, '@')) {
             $public = isset($defaults['public']) ? $defaults['public'] : true;
@@ -410,7 +421,7 @@ class YamlFileLoader extends FileLoader
             }
         }
 
-        $this->container->setDefinition($id, $definition);
+        $this->setDefinition($id, $definition, $isConditionalType);
     }
 
     /**