C# 3.0 - 新功能 - Lambda expressoin

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"=>"這個符號除了代表『等於大於』外，在 C# 3.0 語法中也表示 Lambda expression，它可以讓我們的程式碼更少，也可以讓程式的可讀性更高。

詳細說明：

https://msdn2.microsoft.com/en-us/library/bb397687(VS.90).aspx

完整範例：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace NewLanguageFeatures
{
public class Customer
{
public int CustomerId { get; private set; }

        public string Name { get; set; }
public string City { get; set; }

        public Customer(int Id)
{
CustomerId = Id;
}

        public override string ToString()
{
return Name + "\t" + City + "\t" + CustomerId;
}
}

    class Program
{
static void Main(string[] args)
{
List<Customer> customers = CreateCustomers();

            Console.WriteLine("Customers:\n");

            var customerDictionary = new Dictionary<Customer, string>();

            foreach (var c in customers)
customerDictionary.Add(c, c.Name);

            var matches = customerDictionary.FilterBy(
(customer, name) => name.StartsWith("墩墩"));
           

            foreach (var m in matches)
Console.WriteLine(m);
}

        static List<Customer> CreateCustomers()
{
return new List<Customer>
{
new Customer(1) { Name = "波羅實業", City = "台北市" },
new Customer(2) { Name = "湯姆科技", City = "台中市" },
new Customer(3) { Name = "墩墩數位", City = "高雄市" },
new Customer(4) { Name = "摩利光電", City = "新竹市" },
new Customer(5) { Name = "瑞之路邊攤", City = "花蓮市" }
};
}
}

    public delegate bool KeyValueFilter<K, V>(K key, V value);

    public static class Extensions
{
public static List<K> FilterBy<K, V>(
this Dictionary<K, V> items,
KeyValueFilter<K, V> filter)
{
var result = new List<K>();

            foreach (KeyValuePair<K, V> element in items)
{
if (filter(element.Key, element.Value))
result.Add(element.Key);
}
return result;
}

        public static List<T> Append<T>(this List<T> a, List<T> b)
{
var newList = new List<T>(a);
newList.AddRange(b);
return newList;
}

        public static bool Compare(this Customer customer1, Customer customer2)
{
if (customer1.CustomerId == customer2.CustomerId &&
customer1.Name == customer2.Name &&
customer1.City == customer2.City)
{
return true;
}

            return false;
}
}
}

執行結果：

Customers:

墩墩數位 高雄市 3
Press any key to continue . . .

筆者使用的環境：Windows 2008 RC0 English + Visual Studio 2008