A series of software designs for a BRICS currency platform but also applicable to a set of State-based precious metal depositories running in parallel to the Federal Reserve. Many people expect BRICS to release a gold-backed digital currency for member use but based on their actions, I think the reality will be different.
An important part of design is the top-level pattern and explicit goals. In this case, the pattern (model) is a set of financial realms (countries) executing point-to-point (P2P) transactions, which supports multiple, asymmetrical exchange rates and impedance mismatches between realms.
P2P + visitor is a composition pattern, the opposite of a class hierarchy which needs 80-90% common behavior to work well.