The pimpl idiom (pointer to implementation, sometimes referred to as opaque pointer or cheshire cat technique), reduces the compilation times of a class by moving all its private data members into a struct defined in the .cpp file.
The class owns a pointer to the implementation. This way, it can be forward declared, so that the header file does not need to
#include classes that are used in private member variables.
When using the pimpl idiom, changing a private data member does not require recompiling classes that depend on it.