create per-region std::vector<Route*>s as systems are processed
deterministic mileages
no need for mutex
less region->foo indirection
can avoid a potential HighwaySystem::mileage_by_region function...
...which is not in master or pushed to GitHub as of this writing. Part of an attempt to change:
std::unordered_map<Region*, double> mileage_by_region;
->
std::vector<std::pair<Region*, double>> region_mileages;
std::vector<Route*>s as systems are processedregion->fooindirectionstd::unordered_map<Region*, double> mileage_by_region;->std::vector<std::pair<Region*, double>> region_mileages;