Externalise connected variable cache

[nickerso]

variable equivalence is a common aspect of CellML and many uses outside of libCellML could take advantage of a convenient and fast equivalence cache if it was pulled out of the analyser and made available as a first class part of the libCellML API. Similar to the CellML API's CeVAS service to manage connected variables...

[hsorby]

Currently the existing function is trying to facilitate analysis of the model. The current accessible function may find uses by the user that the developers have not considered, and that its primary function is to facilitate fast equivalent variable lookups for the analyser. The user needs to understand the limitations of this function if they do use if for their own purposes.

[nickerso]

restricted in that its part of the analyser. I'm wondering how hard it would be to pull the equivalence cache out into its own class or maybe part of a model or something... Analysing models can only be done on complete models, whereas variable equivalence can be done any time.

[hsorby]

I don’t think that would be hard at all. Either option model based cache or first class object EquivalentVariableCache would work.

My initial thought would be to have it as a first class object to keep the model as a plain model (arguments here could be made for some of the action API that currently exist on the model). I think I would prefer to see the model become plainer over time and have actioners do work on the model. The equivalent variable cache could be one of those. I expect this would become clearer once some exploratory tests were written.