For regression testing, we can replace our use of expand1.cpp here:

with a .cpp based on @oliverlee's example in gh-2057 perhaps?

So the way this works is:

• Every translation unit gets its own constantInitializer
• When the translation unit gets created (in any order), the constantInitializer increments a global counter
• The global symengine constants are now references, and we allocate them exactly once, using the global counter
• If constantInitializer's destructor ever gets called (not sure if that happens?), we free the global symengine expressions, exactly once.

I think this can work! Thanks @isuruf for implementing it.

Is my understanding at #2059 (comment) correct?

Yep.

(not sure if that happens?)

It gets called when each translation unit gets unloaded and when all translation units are unloaded, the expression is freed. This happens when the program terminates or if we opened the library using dlopen, it happens when the library is closed via dlclose.

@isuruf excellent. (I wasn't sure if this happens when the program terminates, since the OS cleans the memory anyway.)