If you wanted to do things on function exit, you could have an “ENABLE_DEFER” macro that declares a scope for guards; the “DEFER” macro would register the deferred lambda with that scope, not define a new object, and the destructor of the scope would run all the registered guards.

Of course, in my C++ code I would just write a class/struct to wrap any RAII-like logic, not use a “defer”. A marginal amount of extra work that pays off in consistency and readability.