Issue 5258 - Implement Filter::As<>() method to make working with filters easier from C++ code

compiled/subscription/Subscription.h

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 #pragma once
 
-#include <type_traits>
 #include <vector>
 
 #include "../filter/Filter.h"
 #include "../String.h"
 #include "../FilterNotifier.h"
 #include "../intrusive_ptr.h"
 #include "../debug.h"
 #include "../bindings/runtime.h"
 
 #define SUBSCRIPTION_PROPERTY_INTERNAL(field_type, param_type, name, topic, getter, setter) \
@@ skipping 62 matching lines @@
   }
 
   Filter* BINDINGS_EXPORTED FilterAt(Filters::size_type index);
   int BINDINGS_EXPORTED IndexOfFilter(const Filter& filter);
   OwnedString BINDINGS_EXPORTED Serialize() const;
   OwnedString BINDINGS_EXPORTED SerializeFilters() const;
 
   static Subscription* BINDINGS_EXPORTED FromID(const String& id);
 
   template<typename T>
-  T* As();
+  T* As()
+  {
+    if (mType != T::classType)
+      return nullptr;
+
+    return static_cast<T*>(this);
+  }
+
+  template<typename T>
+  const T* As() const
+  {
+    if (mType != T::classType)
+      return nullptr;
+
+    return static_cast<const T*>(this);
+  }
 };
 
 typedef intrusive_ptr<Subscription> SubscriptionPtr;