How to calculate interpolation in animation

In the previous version (Open Cascade 7.7),
I derived a class from AIS_Animation and overrode the Update method.
Within this method, I retrieved the interpolated transformation values using gp_TrsfNLerp myTrsfLerp.

However, in Open Cascade 7.9, this variable has been made private, so it is no longer accessible from the derived class.

As a temporary solution, I declared a new gp_TrsfNLerp variable in the derived class,
initialized it with the initial and final transformations, and used it to calculate the interpolated values for a given progress.

Is there an alternative or recommended way to achieve this in the newer version?