//示例1
(string Alpha, string Beta) namedLetters = ("a", "b");
Console.WriteLine($"{namedLetters.Alpha}, {namedLetters.Beta}");
 //示例2
var alphabetStart = (Alpha: "a", Beta: "b");
Console.WriteLine($"{alphabetStart.Alpha}, {alphabetStart.Beta}");
//示例3
int count = 5;
string label = "Colors used in the map";
var pair = (count, label);
Console.WriteLine(pair);

static (string, double, double) GetLocation() 
 {
    var city = "西安市";
    var lat = 33.42d;
    var lon = 107.40d;
    return (city, lon, lat);
}

//示例4
(string city, double lon, double lat) = GetLocation();
Console.WriteLine($"{city},({lon},{lat})");

(string city, _, _) = GetLocation();
Console.WriteLine($"{city}");

// Expression-bodied constructor
public ExpressionMembersExample(string label) => this.Label = label;

// Expression-bodied finalizer
~ExpressionMembersExample() => Console.Error.WriteLine("Finalized!");

private string label;

// Expression-bodied get / set accessors.
public string Label
{
    get => label;
    set => this.label = value ?? "Default label";
}

public static double ComputeAreaModernIs(object shape)
{
    if (shape is Square s)
        return s.Side * s.Side;
    else if (shape is Circle c)
        return c.Radius * c.Radius * Math.PI;
    else if (shape is Rectangle r)
        return r.Height * r.Length;
    // elided
    throw new ArgumentException(
        message: "shape is not a recognized shape",
        paramName: nameof(shape));
}

public static double ComputeArea_Version3(object shape)
{
    switch (shape)
    {
        case Square s when s.Side == 0:
        case Circle c when c.Radius == 0:
            return 0;

        case Square s:
            return s.Side * s.Side;
        case Circle c:
            return c.Radius * c.Radius * Math.PI;
        default:
            throw new ArgumentException(
                message: "shape is not a recognized shape",
                paramName: nameof(shape));
    }
}

//场景A：条件运算符
string arg = args.Length >= 1 ? args[0] :
    throw new ArgumentException("You must supply an argument");
//场景B：Null合并运算符
public string Name
{
    get => name;
    set => name = value ??
        throw new ArgumentNullException(
          paramName: nameof(value), 
          message: "Name cannot be null");
}
//场景C：Lambda表达式
DateTime ToDateTime(IFormatProvider provider) =>
    throw new InvalidCastException("Conversion to a DateTime is not supported.");

public class ChineseSayHello : ISayHello
{
    public string Who { get; set; }
}

public interface ISayHello
{
    private const string DefaultPersopn = "Anumouse";
    string Who { get; set; }
    void SayHello()
    {
        Who = DefaultPersopn;
         Console.WriteLine($"Hello, {Who}");
    }
 }

//正确，可以编译
var sayHello = new ChineseSayHello() as ISayHello;
sayHello.SayHello();
//错误，无法编译
 var sayHello = new ChineseSayHello();
sayHello.SayHello();

//生成异步流
public static async System.Collections.Generic.IAsyncEnumerable<int> GenerateSequence()
{
    for (int i = 0; i < 20; i++)
    {
        await Task.Delay(100);
        yield return i;
    }
}
//枚举异步流
await foreach (var number in GenerateSequence())
{
    Console.WriteLine(number);
}

var words = new string[]
{
                // index from start index from end
    "The", // 0 ^9
    "quick", // 1 ^8
    "brown", // 2 ^7
    "fox", // 3 ^6
    "jumped", // 4 ^5
    "over", // 5 ^4
    "the", // 6 ^3
    "lazy", // 7 ^2
    "dog" // 8 ^1
};  
//取最后一个元素
Console.WriteLine($"The last word is {words[^1]}");
//获取第一个元素到第三个元素
var quickBrownFox = words[1..4];
//获取倒数第一个元素到倒数第二个元素
var lazyDog = words[^2..^0];
//获取全部元素
var all = words[..];
//获取开始到第三个元素
var firstPhrase = words[..4];
//获取结束到倒数第二个元素
var lastPhrase = words[6..];

record Address
{
    public string Province { get; set; }
    public string City { get; set; }
    public string District { get; set; }
    public string County { get; set; }
}

var addr1 = new Address() { Province = "陕西省", City = "西安市", District = "雁塔区" };
var addr2 = new Address() { Province = "陕西省", City = "西安市", District = "雁塔区" };
Console.WriteLine($"addr1 == addr2：{addr1 == addr2}");

if (addr1.Province == addr2.Province && addr1.City == addr2.City) {
    //属性太多啦，我就不一个一个地比较啦，懂得都懂
}

(province, city, district, county) = addr1;

public record Person
{
    public string LastName { get; }
    public string FirstName { get; }

    public Person(string first, string last) => (FirstName, LastName) = (first, last);
}

var person = new Person("Bill", "Wagner");
Person brother = person with { FirstName = "Paul" }; // 修改FirstName的副本
Person clone = person with { }; // 空集副本

using System;

Console.WriteLine("Hello World!");

System.Console.WriteLine("Hello World!");

public static bool IsLetter(this char c) =>
    c is >= 'a' and <= 'z' or >= 'A' and <= 'Z';

public static bool IsLetterOrSeparator(this char c) =>
    c is (>= 'a' and <= 'z') or (>= 'A' and <= 'Z') or '.' or ',';

if (e is not null)
{
    // ...
}