We make a change:

• from a UniqueFactory QuaternionAlgebra and abstract base class QuaternionAlgebra_abstract
• to an abstract base class QuaternionAlgebra with a __classcall_private__ method

What is done here: We consider QuaternionAlgebraFactory internal and remove it outright. (+ docstring/doctest cosmetics)

Possible implementation variants:

• Minimally invasive change: Keep the UniqueFactory and delegate to it by __classcall_private__. (This was done in c2d2fca)
• Change that maintains full compatibility: Add class methods QuaternionAlgebra.create_key, QuaternionAlgebra.create_object that delegate to the factory functions, so that calls to create_key, create_object continue to work without change
• This could be combined with deprecating QuaternionAlgebraFactory.

Also @saraedum (who introduced the use of UniqueFactory for this class)

• Does UniqueFactory offer any benefits over CachedRepresentation/UniqueRepresentation at all, or should we just replace uses of UniqueFactory by the more commonly used CachedRepresentation/UniqueRepresentation?

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies