Delete traitIf you‘ve encountered this error when using Crubit’s virtual_unique_ptr<T>, note that virtual_unique_ptr<T> is only available when T is a C++ type with a virtual destructor or which overrides operator delete.
When T does not have a virtual destructor and does not override operator delete, use cpp_std::unique_ptr<T> instead.
For types with virtual destructors or custom operator delete implementations, C++'s delete ptr; operation does more than simply destruct the value and free the memory associated with the target type. Instead, C++ will use the custom operator delete defined by the target type.
This makes it possible to convert a std::unique_ptr<DerivedClass> into a std::unique_ptr<BaseClass> so long as BaseClass has a virtual destructor. When the std::unique_ptr<BaseClass> is dropped, the operator delete on the BaseClass will invoke the virtual destructor, resulting in a call to the destructor of DerivedClass. After that, C++ knows to free memory the size of DerivedClass rather than memory the size of BaseClass.
In order to replicate this behavior in Rust, C++'s unique_ptr<T> has been split into two types: unique_ptr and virtual_unique_ptr. unique_ptr assumes that the target type is concrete, while virtual_unique_ptr supports C++ types with a virtual destructor or custom operator delete. Such types will automatically receive a Crubit-generated implementation of the Delete trait.