重構指南 - 儘快返回（Return ASAP ）

儘快返回就是如果方法中的條件判斷可以得到結果，則儘快返回該結果。

1. 檢查條件，如果不滿足就立即返回，不執行下麵的邏輯。

2. 當包含大量的if else嵌套，代碼可讀性變差，也容易出現異常。

3. 在重構時， 儘量使簡單判斷優先執行，儘快返回，提高性能。

代碼重構前

using System.Collections.Generic;
using System.Linq;
using LosTechies.DaysOfRefactoring.SampleCode.BreakMethod.After;
using Customer = LosTechies.DaysOfRefactoring.BreakResponsibilities.After.Customer;

namespace LosTechies.DaysOfRefactoring.SampleCode.ReturnASAP.Before
{
    public class Order
    {
        public Customer Customer { get; private set; }

        public decimal CalculateOrder(Customer customer, IEnumerable<Product> products, decimal discounts)
        {
            Customer = customer;
            decimal orderTotal = 0m;

            if (products.Count() > 0)
            {
                orderTotal = products.Sum(p => p.Price);
                if (discounts > 0)
                {
                    orderTotal -= discounts;
                }
            }

            return orderTotal;
        }
    }
}

代碼重構後

using System.Collections.Generic;
using System.Linq;
using LosTechies.DaysOfRefactoring.SampleCode.BreakMethod.After;
using Customer = LosTechies.DaysOfRefactoring.BreakResponsibilities.After.Customer;

namespace LosTechies.DaysOfRefactoring.SampleCode.ReturnASAP.After
{
    public class Order
    {
        public Customer Customer { get; private set; }

        public decimal CalculateOrder(Customer customer, IEnumerable<Product> products, decimal discounts)
        {
            if (products.Count() == 0)
                return 0;

            Customer = customer;
            decimal orderTotal = products.Sum(p => p.Price);

            if (discounts == 0)
                return orderTotal;

            orderTotal -= discounts;

            return orderTotal;
        }
    }
}

代碼重構後， 可讀性提高，邏輯清晰。