How to model capacity (value and unit) in Domain Driven Design?

Question

If I have a Tank entity, would it be correct to have a Capacity value consisting of Capacity.Value and Capacity.Unit?

I would usually have Tank.CapacityValue and Tank.CapacityUnit, but I think this is not correct in a DDD scenario. Thank you for your input.

Answer 1

I think you're after the Quantity pattern as described here by Martin Fowler:

... But using objects invites us to add new fundamental types whenever they add value, and having a specific type for dimensioned quantities adds quite a lot of value.