One thing that I would like to have is a common base class that can be passed around. Often, I would like for a function orclass to be told which engine to use

One thing that I would like to have is a common base class that can be passed around. Often, I would like for a function orclass to be told which engine to use, quite useful for unit testing, or for having reproducible results. As it is, the only way to accept multiple different engines is by templating over the engine type. This ends up requiring that every part of the code that uses the random engine be brought into the header file, and classes need to be templated on the engine type to store a reference to the engine. I was kind of hoping that the `random_generator` class would be a templated class derived from a non-templated base class, so that it could be used in this manner. Looking over it, I can see why it doesn't, as many of the methods are much, much more useful as templated methods, which do not interact nicely with virtual functions.