Lean Architecture for Agile Software Development

Appendix C. Account Example in C#

Christian Horsdal Gammelgaard provides the following code in C#, using the extension method facility as a way to demonstrate injection of role functionality into a domain class.

using System;

namespace DCI
{
    // Methodless role types
    public interface TransferMoneySink
    {
    }

    // Methodful roles
    public interface TransferMoneySource
    {
    }

    public static class TransferMoneySourceTraits
    {

        public static void TransferFrom(
                this TransferMoneySource self,
                TransferMoneySink recipient, double amount)
        {
            // This methodful role can only
            // be mixed into Account object (and subtypes)

Account self_=self as Account;
            Account recipient_=recipient as Account;

            // Self-contained readable and testable
            // algorithm

            if (self_ != null && recipient_ != null)
            {
                self_.DecreaseBalance(amount);
                self_.Log("Withdrawing " + amount);
                recipient_.IncreaseBalance(amount);
                recipient_.Log("Depositing " + amount);
            }
         }
      }


     // Context object
     public class TransferMoneyContext
     {
         // Properties for accessing the concrete objects
         // relevant in this context through their
         // methodless roles
         public TransferMoneySource Source {
             get; private set;
         }

         public TransferMoneySink Sink {
             get;
             private set;
         }

         public double Amount {
             get; private set;
         }

         public TransferMoneyContext()
         {
             // logic for retrieving source and sink accounts
         }

         public TransferMoneyContext(
                         TransferMoneySource source,

TransferMoneySink sink, double amount) { Source = source; Sink = sink; Amount = amount; } public void Doit() { Source.TransferFrom(Sink, ...