I asked this question yesterday: Equality comparison for a surname value object class. The answerer advised that it was pointless creating a Surname Value Object and I tend to agree.

There are two benefits of removing Primitive Obsession by introducing a Value Object:

1) It makes the Domain Model more explicit. For example, I can talk to a business analyst about a Post Code instead of a string that contains a post code.

2) All the validation is in one place instead of across the application.

I believe it is point two that is pointless (because there is not enough validation logic). Please see the code below:

using Cost = System.Decimal; public class CurrencyCalculator {     private readonly ICurrency currency;     public CurrencyCalculator(ICurrency currency)     {         this.currency = currency;     }      public IEnumerable<KeyValuePair<int, int>> CalculateDenominationsFor(Cost cost)      {         var target = cost;         foreach (var denomination in currency.AvailableDenominations.OrderByDescending(a => a))         {            var numberRequired = target / denomination;            if (numberRequired > 0)            {                yield return new KeyValuePair<int, int>(denomination, numberRequired);            }            target = target - (numberRequired * denomination);          }     }  } 

Notice that CalculateDenominationsFor is now accepting a Cost instead of a decimal (because of the type alias).

Q1) Is this normal practice?

Q2) Does this make the Domain Model more explicit without over engineering it by creating a Cost class (Value Object)?

Q3) Are there any pitfalls to this approach?