check for drop func

CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.25)
-project(blt-gp VERSION 0.0.138)
+project(blt-gp VERSION 0.0.139)
 
 include(CTest)
 

include/blt/gp/program.h

@@ -150,7 +150,10 @@ namespace blt::gp
                             alloc.call_destructors<Args...>(mask);
                             break;
                         case detail::destroy_t::RETURN:
-                            alloc.from<detail::remove_cv_ref<Return>>(0).drop();
+                            if constexpr (detail::has_func_drop_v<remove_cvref_t<Return>>)
+                            {
+                                alloc.from<detail::remove_cv_ref<Return>>(0).drop();
+                            }
                             break;
                     }
                 });