public static void OtherInterestingFeatures()
{
// OPTIONAL PARAMETERS
MethodSignatures(3, 1, 3, "Some", "Extra", "Strings");
MethodSignatures(3, another: 3); // explicity set a parameter, skipping optional ones
// EXTENSION METHODS
int i = 3;
i.Print(); // Defined below
// NULLABLE TYPES - great for database interaction / return values
// any value type (i.e. not a class) can be made nullable by suffixing a ?
// <type>? <var name> = <value>
int? nullable = null; // short hand for Nullable<int>
Console.WriteLine("Nullable variable: " + nullable);
bool hasValue = nullable.HasValue; // true if not null
// ?? is syntactic sugar for specifying default value (coalesce)
// in case variable is null
int notNullable = nullable ?? 0; // 0
// IMPLICITLY TYPED VARIABLES - you can let the compiler work out what the type is:
var magic = "magic is a string, at compile time, so you still get type safety";
// magic = 9; will not work as magic is a string, not an int
// TEMPLATES
var phonebook = new Dictionary<string, string>() {
{"Sarah", "212 555 5555"} // Add some entries to the phone book
};
// Calling SETDEFAULT defined as a template above
Console.WriteLine(SetDefault<string,string>(phonebook, "Shaun", "No Phone")); // No Phone
// nb, you don't need to specify the TKey and TValue since they can be
// derived implicitly
Console.WriteLine(SetDefault(phonebook, "Sarah", "No Phone")); // 212 555 5555
// LAMBDA EXPRESSIONS - allow you to write code in line
Func<int, int> square = (x) => x * x; // Last T item is the return value
Console.WriteLine(square(3)); // 9
// PARALLEL FRAMEWORK
// http://blogs.msdn.com/b/csharpfaq/archive/2010/06/01/parallel-programming-in-net-framework-4-getting-started.aspx
var websites = new string[] {
"http://www.google.com", "http://www.reddit.com",
"http://www.shaunmccarthy.com"
};
var responses = new Dictionary<string, string>();
// Will spin up separate threads for each request, and join on them
// before going to the next step!
Parallel.ForEach(websites,
new ParallelOptions() {MaxDegreeOfParallelism = 3}, // max of 3 threads
website =>
{
// Do something that takes a long time on the file
using (var r = WebRequest.Create(new Uri(website)).GetResponse())
{
responses[website] = r.ContentType;
}
});
// This won't happen till after all requests have been completed
foreach (var key in responses.Keys)
Console.WriteLine("{0}:{1}", key, responses[key]);
// DYNAMIC OBJECTS (great for working with other languages)
dynamic student = new ExpandoObject();
student.FirstName = "First Name"; // No need to define class first!
// You can even add methods (returns a string, and takes in a string)
student.Introduce = new Func<string, string>(
(introduceTo) => string.Format("Hey {0}, this is {1}", student.FirstName, introduceTo));
Console.WriteLine(student.Introduce("Beth"));
// IQUERYABLE<T> - almost all collections implement this, which gives you a lot of
// very useful Map / Filter / Reduce style methods
var bikes = new List<Bicycle>();
bikes.Sort(); // Sorts the array
bikes.Sort((b1, b2) => b1.Wheels.CompareTo(b2.Wheels)); // Sorts based on wheels
var result = bikes
.Where(b => b.Wheels > 3) // Filters - chainable (returns IQueryable of previous type)
.Where(b => b.IsBroken && b.HasTassles)
.Select(b => b.ToString()); // Map - we only this selects, so result is a IQueryable<string>
var sum = bikes.Sum(b => b.Wheels); // Reduce - sums all the wheels in the collection
// Create a list of IMPLICIT objects based on some parameters of the bike
var bikeSummaries = bikes.Select(b=>new { Name = b.Name, IsAwesome = !b.IsBroken && b.HasTassles });
// Hard to show here, but you get type ahead completion since the compiler can implicitly work
// out the types above!
foreach (var bikeSummary in bikeSummaries.Where(b => b.IsAwesome))
Console.WriteLine(bikeSummary.Name);
// ASPARALLEL
// And this is where things get wicked - combines linq and parallel operations
var threeWheelers = bikes.AsParallel().Where(b => b.Wheels == 3).Select(b => b.Name);
// this will happen in parallel! Threads will automagically be spun up and the
// results divvied amongst them! Amazing for large datasets when you have lots of
// cores
// LINQ - maps a store to IQueryable<T> objects, with delayed execution
// e.g. LinqToSql - maps to a database, LinqToXml maps to an xml document
var db = new BikeRespository();
// execution is delayed, which is great when querying a database
var fitler = db.Bikes.Where(b => b.HasTassles); // no query run
if (42 > 6) // You can keep adding filters, even conditionally - great for "advanced search" functionality
fitler = fitler.Where(b => b.IsBroken); // no query run
var query = fitler
.OrderBy(b => b.Wheels)
.ThenBy(b => b.Name)
.Select(b => b.Name); // still no query run
// Now the query runs, but opens a reader, so only populates are you iterate through
foreach (string bike in query)
Console.WriteLine(result);
}
public static void OtherInterestingFeatures()
{
// 可选参数
MethodSignatures(3, 1, 3, "Some", "Extra", "Strings");
MethodSignatures(3, another: 3); // 显式指定参数，忽略可选参数
// 扩展方法
int i = 3;
i.Print(); // 参见下面的定义
// 可为null的类型 对数据库交互、返回值很有用
// 任何值类型 (i.e. 不为类) 添加后缀 ? 后会变为可为null的值
// <类型>? <变量名> = <值>
int?nullable = null; // Nullable<int> 的简写形式
Console.WriteLine("Nullable variable: " + nullable);
bool hasValue = nullable.HasValue; // 不为null时返回真
// ?? 是用于指定默认值的语法糖
// 以防变量为null的情况
int notNullable = nullable ?? 0; // 0
// 变量类型推断 - 你可以让编译器推断变量类型:
var magic = "编译器确定magic是一个字符串，所以仍然是类型安全的";
// magic = 9; // 不工作，因为magic是字符串，而不是整数。
// 泛型
//
var phonebook = new Dictionary <string, string>()
{
{ "Sarah", "212 555 5555" } // 在电话簿中加入新条目
};
// 调用上面定义为泛型的SETDEFAULT
Console.WriteLine(SetDefault <string, string>(phonebook, "Shaun", "No Phone")); // 没有电话
// 你不用指定TKey、TValue，因为它们会被隐式地推导出来
Console.WriteLine(SetDefault(phonebook, "Sarah", "No Phone")); // 212 555 5555
// lambda表达式 - 允许你用一行代码搞定函数
Func <int, int> square = (x) => x * x; // 最后一项为返回值
Console.WriteLine(square(3)); // 9
// 可抛弃的资源管理 - 让你很容易地处理未管理的资源
// 大多数访问未管理资源 (文件操作符、设备上下文, etc.)的对象
// 都实现了IDisposable接口。
// using语句会为你清理IDisposable对象。
using (StreamWriter writer = new StreamWriter("log.txt"))
{
writer.WriteLine("这里没有什么可疑的东西");
// 在作用域的结尾，资源会被回收
// （即使有异常抛出，也一样会回收）
}
// 并行框架
// http://blogs.msdn.com/b/csharpfaq/archive/2010/06/01/parallel-programming-in-net-framework-4-getting-started.aspx
var websites = new string[] {
"http://www.google.com", "http://www.reddit.com",
"http://www.shaunmccarthy.com"
};
var responses = new Dictionary <string, string>();
// 为每个请求新开一个线程
// 在运行下一步前合并结果
Parallel.ForEach(websites,
new ParallelOptions()
{
MaxDegreeOfParallelism = 3
}, // max of 3 threads
website =>
{
// Do something that takes a long time on the file
using (var r = WebRequest.Create(new Uri(website)).GetResponse())
{
responses[website] = r.ContentType;
}
});
// 直到所有的请求完成后才会运行下面的代码
foreach (var key in responses.Keys)
{
Console.WriteLine("{0}:{1}", key, responses[key]);
}
// 动态对象（配合其他语言使用很方便）
dynamic student = new ExpandoObject();
student.FirstName = "First Name"; // 不需要先定义类！
// 你甚至可以添加方法（接受一个字符串，输出一个字符串）
student.Introduce = new Func <string, string>(
(introduceTo) => string.Format("Hey {0}, this is {1}", student.FirstName, introduceTo));
Console.WriteLine(student.Introduce("Beth"));
// IQUERYABLE<T> - 几乎所有的集合都实现了它，
// 带给你 Map / Filter / Reduce 风格的方法
var bikes = new List <Bicycle>();
bikes.Sort(); // Sorts the array
bikes.Sort((b1, b2) => b1.Wheels.CompareTo(b2.Wheels)); // 根据车轮数排序
var result = bikes
.Where(b => b.Wheels > 3) // 筛选 - 可以连锁使用 （返回IQueryable)
.Where(b => b.IsBroken && b.HasTassles)
.Select(b => b.ToString()); // Map - 这里我们使用了select，所以结果是IQueryable<string>
var sum = bikes.Sum(b => b.Wheels); // Reduce - 计算集合中的轮子总数
// 创建一个包含基于自行车的一些参数生成的隐式对象的列表
var bikeSummaries = bikes.Select(b => new { Name = b.Name, IsAwesome = !b.IsBroken && b.HasTassles });
// 很难演示，但是编译器在代码编译完成前就能推导出以上对象的类型
foreach (var bikeSummary in bikeSummaries.Where(b => b.IsAwesome))
{
Console.WriteLine(bikeSummary.Name);
}
// ASPARALLEL
// 邪恶的特性 —— 组合了linq和并行操作
var threeWheelers = bikes.AsParallel().Where(b => b.Wheels == 3).Select(b => b.Name);
// 以上代码会并发地运行。会自动新开线程，分别计算结果。
// 适用于多核、大数据量的场景。
// LINQ - 将IQueryable<T>映射到存储，延缓执行
// 例如 LinqToSql 映射数据库, LinqToXml 映射XML文档
var db = new BikeRespository();
// 执行被延迟了，这对于查询数据库来说很好
var filter = db.Bikes.Where(b => b.HasTassles); // 不运行查询
if (42 > 6) // 你可以不断地增加筛选，包括有条件的筛选，例如用于“高级搜索”功能
{
filter = filter.Where(b => b.IsBroken); // 不运行查询
}
var query = filter
.OrderBy(b => b.Wheels)
.ThenBy(b => b.Name)
.Select(b => b.Name); // 仍然不运行查询
// 现在运行查询，运行查询的时候会打开一个读取器，所以你迭代的是一个副本
foreach (string bike in query)
{
Console.WriteLine(result);
}
}