添加ObjectPtr定义，准备全面加入指针

include/context.hpp

@@ -115,7 +115,7 @@ namespace Fig
                 throw RuntimeError(FStringView(std::format("Variable '{}' not defined", name.toBasicString())));
             }
         }
-        void def(const FString &name, const TypeInfo &ti, AccessModifier am, const Object &value = Any())
+        void def(const FString &name, const TypeInfo &ti, AccessModifier am, const Object &value = Object::getNullInstance())
         {
             if (containsInThisScope(name))
             {

include/value.hpp

@@ -441,5 +441,5 @@ namespace Fig
         }
     };
 
-    using Any = Object;
+    using ObjectPtr = std::shared_ptr<Object>;
 } // namespace Fig