Use common investment rule function

[nailend]

There are duplicated rule formulations in the investment blocks of flows, _generic_storage and SinkDSM which only differ slightly with their indexes and constraint name. This counts for:

• _old_storage_capacity_rule_end
• _old_dsm_capacity_rule_end (for every SinkDSM approach)
• _old_capacity_rule_end

Is there a way to define a common function which is called inside and indexes and constraint are passed. The advantage would be, that if anything changes, not five different code-locations have to be changed and checked. I just encountered this problem in #957

[p-snft]

Thanks for bringing this up. I'd suggest to split _options.py into a submodule. The constraints would then be formulated in options/_investment.py that bundles the class Investment and the constraints (and analogue for NonConvex).

[jokochems]

There are duplicated rule formulations in the investment blocks of flows, _generic_storage and SinkDSM which only differ slightly with their indexes and constraint name. This counts for:

• _old_storage_capacity_rule_end
• _old_dsm_capacity_rule_end (for every SinkDSM approach)
• _old_capacity_rule_end

Is there a way to define a common function which is called inside and indexes and constraint are passed. The advantage would be, that if anything changes, not five different code-locations have to be changed and checked. I just encountered this problem in #957

I agree that this would be sensible and facilitate code maintenance as well as development of new functionality.