Build a BusAllocation by asking count for each type — the one spelling of the field-by-field construction (compile-checked total by the return type), so a builder in another module cannot silently skip a newly added bus type.
count
Build a BusAllocation by asking
countfor each type — the one spelling of the field-by-field construction (compile-checked total by the return type), so a builder in another module cannot silently skip a newly added bus type.