Side Effect Free Functions

A.Refactoring_To_Side_Effect_Free_Functions.cs

  public class CartService 
	{
		public decimal GetShippingQuoteForUpdatedAddress(ShoppingCart cart,
		                                                 Address updatedAddress)
		{
			cart.CalculateShippingDetail(updatedAddress); //Side effect
			return cart.ShippingQuote;
		}
	}

B.ShoppingCart-PreRefactoring.cs

	public class ShoppingCart : IEntity
	{
		public string ShoppingCartCode { get; }

		public IEnumerable<string> Products { get; set; }
        
		public decimal ShippingQuote { get; private set; }

		public string ShippingMethod { get; private set; }

		public void CalculateShippingDetail(Address customerAddress)
		{
			//Some Complex Calculations here that cause a side effect

			ShippingQuote = 20.3m;
			ShippingMethod = "Next Day Air";
		}
	}

C.Refactored-ShippingDetail.cs

  public class ShippingDetail //Refactoring the ShippingDetail to a value object
	{
		public ShippingDetail(decimal shippingQuote, string shippingMethod) 
		{
			ShippingQuote = shippingQuote;
			ShippingMethod = shippingMethod;
		}

		public decimal ShippingQuote { get; private set; }

		public string ShippingMethod { get; private set; }

		public ShippingDetail Calculate(Address customerAddress, 
		                                IEnumerable<string> Products)
		{
			//Some Complex Calculations here

			return new ShippingDetail(20.3m, "Next Day Air");
		}
	}

D.Refactored-ShoppingCart.cs

	public class ShoppingCart : IEntity
	{
		public string ShoppingCartCode { get; }

		public IEnumerable<string> Products { get; set; }
        
		public ShippingDetail ShippingDetail { get; set; }

		public void CalculateShippingDetail(Address customerAddress)
		{
			ShippingDetail = ShippingDetail.Calculate(customerAddress, Products);
		}
	}

E.Updated-Cart-Service.cs

  public class CartService 
	{
		public decimal GetShippingQuoteForUpdatedAddress(ShoppingCart cart,
		                                                 Address updatedAddress)
		{
			var detail = cart.ShippingDetail.Calculate(updatedAddress, cart.Products);

			return detail.ShippingQuote;
		}
	}