QScopedPointer usage with Forward Declaration

[peppermg]

From the Qt documentation

Classes that are forward declared can be used within QScopedPointer, as long as the destructor of the forward declared class is available whenever a QScopedPointer needs to clean up.

Concretely, this means that all classes containing a QScopedPointer that points to a forward declared class must have non-inline constructors, destructors and assignment operators

I believe the issue is the compiler will implicitly define a default constructor in places where your type is still incomplete causing the error.