.NetCore3.1 升级 .Net5 c#6 c#7 c#8 c#9 新语法

vs版本：16.8

下载地址：https://dotnet.microsoft.com/download/dotnet/5.0

解决方案选择.net 5 升级完成

c#6新语法

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

namespace SharpGrammarInfo.SharpSix
{
    public class Student
    {
        public Student(string firstName, string lastName)
        {
            FirstName = firstName;
            LastName = lastName;
        }

        public int? Id { get; set; }

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

        //对只读属性只能通过构造函数对其初始化值
        //public void SetName(string firstName, string lastName)
        //{
        //    FirstName = firstName;
        //    LastName = lastName;
        //}


        //自动属性初始化表达式
        public ICollection<double> Grades { get; } = new List<double>();

        //public override string ToString() => $"{LastName}, {FirstName}";
        public override string ToString() => $"{FirstName}-{LastName}";

        //c#6 新写法 只读自动属性
        public string FullName => $"{FirstName}-{LastName}";

        //c#6 新写法 只读自动属性
        public string FullName1
        {
            get
            {
                return $"{FirstName}-{LastName}";
            }
        }
    //老写法
        public string TestName { get; set; }
    }
}

c#7新语法

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading.Tasks;

namespace SharpGrammarInfo.SharpSeven
{
    public class SharpSevenInfo
    {
        public static void Show()
        {

            #region Out变量
            {
                ////不需要声明
                //string input = Console.ReadLine(); 
                //int.TryParse(input, out int result);
                //Console.WriteLine(result);

                ////out 修改是可以是var类型声明
                //int.TryParse(input, out var result1);
                //Console.WriteLine(result1);

                //Console.WriteLine("****************Out*****************");

                ////out 变量
                //DInfo dInfo = new DInfo(123);

            }
            #endregion

            #region 元组
            {
                (string Alpha, string Beta) namedLetters = ("a", "b");
                namedLetters.Alpha = "aa";
                namedLetters.Beta = "bb";
                Console.WriteLine($"{namedLetters.Alpha}, {namedLetters.Beta}");

                var alphabetStart = (Alpha: "a", Beta: "b");
                alphabetStart.Beta = "B+B";
                alphabetStart.Alpha = "A+A";
                Console.WriteLine($"{alphabetStart.Alpha}, {alphabetStart.Beta}");

                (int max, int min) = Range();
                Console.WriteLine(max);
                Console.WriteLine(min);
            }
            {
                var p = new Point(12, 13);
                Console.WriteLine(p.X);
                Console.WriteLine(p.Y);
                p.Deconstruct(out double xx, out double yy);
                Console.WriteLine(xx);
                Console.WriteLine(yy);
            }
            #endregion

            #region 弃元
            {
                var (_, _, _, pop1, _, pop2) = QueryCityDataForYears("New York City", 1960, 2010);
                (string, double, int, int, int, int) result = QueryCityDataForYears("New York City", 1960, 2010);
            }
            #endregion

            #region 模式 
            {
                int input = 123;
                int sum = 234;
                if (input is int count)
                    sum += count;
            }
            {
                //IEnumerable<object> enumerablelist = new List<object>()
                //{
                //    0,
                //    new List<int>(){ 0,1,2,3,4,5,6 },
                //    100,
                //    null
                //};
                //int iResult = SumPositiveNumbers(enumerablelist);
            }



            #region 本地方法
            LocalFunction("朝夕教育");
            #endregion

            //#region  expression-bodied 成员
            //ExpressionMembersExample expression = new ExpressionMembersExample("朝夕教育");
            //#endregion

            //#region throw 表达式
            //string[] args = new string[] { "zhaoxi01", "zhaoxi02", "zhaoxi03" };
            //string arg = args.Length >= 4 ? args[0] :
            //                 throw new ArgumentException("You must supply an argument");
            //#endregion

            #region 默认文本表达式
            Func<string, bool> whereClause = default(Func<string, bool>);
            Func<string, bool> whereClause1 = default;
            #endregion

            #region 数字文本语法改进

            //二进制数形式写入
            //误读的数值常量可能使第一次阅读代码时更难理解。 位掩码或其他符号值容易产生误解。 C# 7.0 包括两项新功能，可用于以最可读的方式写入数字来用于预期用途：二进制文本和数字分隔符 。
            //在创建位掩码时，或每当数字的二进制表示形式使代码最具可读性时，以二进制形式写入该数字
            int Sixteen = 0b0001_0000;
            Console.WriteLine(Sixteen);
            int ThirtyTwo = 0b0010_0000;
            Console.WriteLine(ThirtyTwo);
            int SixtyFour = 0b0100_0000;
            Console.WriteLine(SixtyFour);
            int OneHundredTwentyEight = 0b1000_0000;
            Console.WriteLine(OneHundredTwentyEight);

            //long类型
            //常量开头的 0b 表示该数字以二进制数形式写入。 二进制数可能会很长，因此通过引入 _ 作为数字分隔符通常更易于查看位模式，如前面示例中的二进制常量所示。 数字分隔符可以出现在常量的任何位置。 对于十进制数字，通常将其用作千位分隔符。 十六进制和二进制文本可采用 _ 开头：
            long BillionsAndBillions = 100_000_000_000;
            Console.WriteLine(BillionsAndBillions);
            //decimal、float 和 double 
            //数字分隔符也可以与 decimal、float 和 double 类型一起使用：
            double AvogadroConstant = 6.022_140_857_747_474e23;
            Console.WriteLine(AvogadroConstant);
            decimal GoldenRatio = 1.618_033_988_749_894_848_204_586_834_365_638_117_720_309_179M;
            Console.WriteLine(GoldenRatio);
            #endregion

            #region 命名实参
            //  该方法可以通过使用位置参数以正常方式调用。
            PrintOrderDetails("Gift Shop", 31, "Red Mug");

            // 可以按任何顺序为参数提供命名参数。
            PrintOrderDetails(orderNum: 31, productName: "Red Mug", sellerName: "Gift Shop");
            PrintOrderDetails(productName: "Red Mug", sellerName: "Gift Shop", orderNum: 31);

            // 与位置参数混合的命名参数有效 
            // 只要它们被使用在正确的位置。
            PrintOrderDetails("Gift Shop", 31, productName: "Red Mug");
            PrintOrderDetails(sellerName: "Gift Shop", 31, productName: "Red Mug");    // C# 7.2 onwards
            PrintOrderDetails("Gift Shop", orderNum: 31, "Red Mug");                   // C# 7.2 onwards

            ////但是，如果使用顺序错误，则混合参数无效。
            //// 以下语句将导致编译器错误。
            //PrintOrderDetails("Gift Shop", 31, productName: "Red Mug");
            //PrintOrderDetails(31, sellerName: "Gift Shop", "Red Mug");
            //PrintOrderDetails(31, "Red Mug", sellerName: "Gift Shop");
            #endregion


            #region private protected 访问修饰符---新复合访问修饰符
            // 访问修饰符是关键字，用于指定成员或类型已声明的可访问性。 本部分介绍四个访问修饰符： 
            //可使用访问修饰符指定以下六个可访问性级别：
            //public：访问不受限制。
            //protected：访问限于包含类或派生自包含类的类型。
            //internal：访问限于当前程序集。
            //protected internal：访问限于当前程序集或派生自包含类的类型。
            //private：访问限于包含类。

            //C#7特有
            //private protected：访问限于包含类或当前程序集中派生自包含类的类型。
            #endregion



            #region 增强的泛型约束

            ///之前讲的泛型约束有几种？
            //枚举做基类约束
            GerenicInfo<EnumInfo> info = new GerenicInfo<EnumInfo>();
            info.Show(EnumInfo.ONE);

            //约束不能为空
            GerenicInfoUnmanaged<int> gerenicInfoUnmanaged = new GerenicInfoUnmanaged<int>();
            //GerenicInfoUnmanaged<string> gerenicInfoUnmanaged = new GerenicInfoUnmanaged<string>(); 
            #endregion


            #region 通用的异步返回类型

            //ValueTask<int> task = Func();
            //await foreach (var item in task)
            //{

            //}
            #endregion

        }

        public static async ValueTask<int> Func()
        {
            await Task.Delay(100);
            return 5;
        }


        /// <summary>
        /// 
        /// </summary>
        /// <typeparam name="T"></typeparam>
        public class GerenicInfo<T> where T : Enum
        {
            public void Show(T t)
            {

            }
        }

        public enum EnumInfo
        {
            ONE,
            TOWN,
            THREE
        }

        public class GerenicInfoUnmanaged<T> where T : unmanaged
        {
            public void Show(T t)
            {

            }
        }



        public static ref int FindRef(int[,] matrix, Func<int, bool> predicate)
        {
            for (int i = 0; i < matrix.GetLength(0); i++)
            {
                for (int j = 0; j < matrix.GetLength(1); j++)
                {
                    if (predicate(matrix[i, j]))
                    {
                        return ref matrix[i, j];
                    }

                }
            }
            throw new InvalidOperationException("Not found");
        }


        public static void PrintOrderDetails(string sellerName, int orderNum, string productName)
        {
            if (string.IsNullOrWhiteSpace(sellerName))
            {
                throw new ArgumentException(message: "Seller name cannot be null or empty.", paramName: nameof(sellerName));
            }

            Console.WriteLine($"Seller: {sellerName}, Order #: {orderNum}, Product: {productName}");
        }


        public static string LocalFunction(string name)
        {
            return ZhxiToString(name);

            string ZhxiToString(string name)
            {
                return name;
            }
        }

        /// <summary>
        /// Ref 局部变量和返回结果
        /// </summary>
        /// <param name="matrix"></param>
        /// <param name="predicate"></param>
        /// <returns></returns>
        public static ref int Find(int[,] matrix, Func<int, bool> predicate)
        {
            for (int i = 0; i < matrix.GetLength(0); i++)
                for (int j = 0; j < matrix.GetLength(1); j++)
                    if (predicate(matrix[i, j]))
                        return ref matrix[i, j];
            throw new InvalidOperationException("Not found");
        }


        /// <summary>
        /// 模式
        /// </summary>
        /// <param name="sequence"></param>
        /// <returns></returns>
        public static int SumPositiveNumbers(IEnumerable<object> sequence)
        {
            int sum = 0;
            foreach (var i in sequence)
            {
                switch (i)
                {
                    case 0:
                        break;
                    case IEnumerable<int> childSequence:
                        {
                            foreach (var item in childSequence)
                                sum += (item > 0) ? item : 0;
                            break;
                        }
                    case int n when n > 0:
                        sum += n;
                        break;
                    case null:
                        throw new NullReferenceException("Null found in sequence");
                    default:
                        throw new InvalidOperationException("Unrecognized type");
                }
            }
            return sum;
        }


        private static (string, double, int, int, int, int) QueryCityDataForYears(string name, int year1, int year2)
        {
            int population1 = 0, population2 = 0;
            double area = 0;

            if (name == "New York City")
            {
                area = 468.48;
                if (year1 == 1960)
                {
                    population1 = 7781984;
                }
                if (year2 == 2010)
                {
                    population2 = 8175133;
                }
                return (name, area, year1, population1, year2, population2);
            }

            return ("", 0, 0, 0, 0, 0);
        }


        private static (int max, int min) Range()
        {
            return (123, 234);
        }
    }


    public class Point
    {
        public Point(double x, double y)
            => (X, Y) = (x, y);

        public double X { get; }
        public double Y { get; }

        public void Deconstruct(out double x, out double y) =>
            (x, y) = (X, Y);
    }


    public class BInfo
    {
        public BInfo(int i, out string j)
        {
            j = i.ToString();
        }
    }

    public class DInfo : BInfo
    {
        public DInfo(int i) : base(i, out var j)
        {
            Console.WriteLine($"The value of 'j' is {j}");
        }
    }

    #endregion

}

c#8新语法

 
using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace SharpGrammarInfo.SharpEight
{
    /// <summary>
    /// C#8
    /// </summary>
    public class SharpEightInfo
    {
        public static void Show()
        {
            #region 默认接口方法
            CustomInterface interface1 = new CustomClass();
            interface1.Show();
            interface1.ShowInfo();
            #endregion

            #region switch 表达式

            //老玩法
            string week3 = WeekToStringSwitch(WeekInfo.Monday);
            string week4 = WeekToStringSwitch(WeekInfo.Tuesday);
            string week5 = WeekToStringSwitch(WeekInfo.Wednesday);

            //新玩法
            string week = WeekToString(WeekInfo.Wednesday);
            string week1 = WeekToString(WeekInfo.Tuesday);
            string week2 = WeekToString(WeekInfo.Wednesday);
            #endregion

            #region 属性模式
            PropertyPattern product = new PropertyPattern()
            {
                ProductName = "朝夕架构班",
                Price = 5499
            };
            PropertyPattern product1 = new PropertyPattern()
            {
                ProductName = "朝夕高级班",
                Price = 4299
            };
            double price = PropertyPatternShow(product);
            #endregion

            #region 元组模式
            string strResult = RockPaperScissors("朝夕", "教育1");
            string strResult1 = RockPaperScissors("朝夕", "教育");

            string strResult3 = RockPaperScissors("朝夕", "教育3");
            #endregion

            #region 位置模式
            PointInfo point = new PointInfo(123, 234);
            int i = 11;
            int j = 12;
            point.Deconstruct(out i, out j);
            #endregion

             

            #region 静态本地函数 
            M();

            static int M()
            {
                int y = 5;
                int x = 7;
                return Add(x, y);

                static int Add(int left, int right) => left + right;
            }
            #endregion

            #region 可空引用类型
            //string? str = null;
            //string str1 = null;

            #endregion
             
            #region 异步流
            AsyncIEnumerableShow();
            #endregion

        }

        /// <summary>
        /// C#8新语法
        /// 如果enum是summation类型的话其实｜也可以不需要｜｜
        /// </summary>
        /// <param name="week"></param>
        /// <returns></returns>
        public static string WeekToString(WeekInfo week) => week switch
        {
            WeekInfo.Monday | WeekInfo.Tuesday => "周一",//正常使用
            WeekInfo.Wednesday or WeekInfo.Thursday => "周三",//编译不报错 运行时报错
            WeekInfo.Friday => "周五",
            WeekInfo.Saturday => "周六",
            WeekInfo.Sunday => "周七",
            _ => throw new NotImplementedException("枚举不存在"),
        };

        /// <summary>
        ///switch 经典switch
        /// </summary>
        /// <param name="week"></param>
        /// <returns></returns>
        public static string WeekToStringSwitch(WeekInfo week)
        {
            switch (week)
            {
                case WeekInfo.Monday:
                    return "周一";

                case WeekInfo.Tuesday:
                    return "周二";

                case WeekInfo.Wednesday:
                    return "周三";

                case WeekInfo.Thursday:
                    return "周四";

                case WeekInfo.Friday:
                    return "周五";

                case WeekInfo.Saturday:
                    return "周六";

                case WeekInfo.Sunday:
                    return "周七";

                default:
                    throw new NotImplementedException("枚举不存在");

            }
        }

        /// <summary>
        ///switch 属性模式
        /// </summary>
        /// <param name="pattern"></param>
        /// <returns></returns>
        public static double PropertyPatternShow(PropertyPattern pattern) => pattern
            switch
        {
            { ProductName: "朝夕架构班" } => pattern.Price * 0.5,
            _ => throw new NotImplementedException(),
        };

        /// <summary>
        /// switch 元组模式
        /// </summary>
        /// <param name="first"></param>
        /// <param name="second"></param>
        /// <returns></returns>
        public static string RockPaperScissors(string first, string second)
    => (first, second) switch
    {
        ("朝夕", "教育1") => $"{first}-{second}",
        ("朝夕", "教育2") => $"{first}-{second}",
        ("朝夕", "教育3") => $"{first}-{second}",
        (_, _) => "不匹配"
    };

        /// <summary>
        /// using 声明
        /// </summary>
        /// <param name="lines"></param>
        /// <returns></returns>
        public static int WriteLinesToFile(IEnumerable<string> lines)
        {
            {
                using (var file1 = new System.IO.StreamWriter("WriteLines2.txt"))
                {

                    int skippedLines1 = 0;
                    foreach (string line in lines)
                    {
                        if (!line.Contains("Second"))
                        {
                            file1.WriteLine(line);
                        }
                        else
                        {
                            skippedLines1++;
                        }
                    }
                    // Notice how skippedLines is in scope here.
                    return skippedLines1;
                    // file is disposed here
                }

            }
            {
                using var file = new System.IO.StreamWriter("WriteLines2.txt");
                int skippedLines = 0;
                foreach (string line in lines)
                {
                    if (!line.Contains("Second"))
                    {
                        file.WriteLine(line);
                    }
                    else
                    {
                        skippedLines++;
                    }
                }
                // Notice how skippedLines is in scope here.
                return skippedLines;
                // file is disposed here
            }
        }

        /// <summary>
        /// 异步流
        /// </summary>
        public async static void AsyncIEnumerableShow()
        {
            Console.WriteLine("********************异步流*********************");
            IAsyncEnumerable<int> asynclist = GenerateSequence();
            await foreach (var item in asynclist)
            {
                Console.WriteLine(item);
            }
            Console.WriteLine("********************异步流*********************");
        }


        public static async IAsyncEnumerable<int> GenerateSequence()
        {
            for (int i = 0; i < 20; i++)
            {
                await Task.Delay(1000).ContinueWith(s =>
                {
                    Console.WriteLine($"线程ID:{Thread.CurrentThread.ManagedThreadId.ToString("000")}");
                });
                yield return i;
            }
        }
    }

    public enum WeekInfo
    {
        Monday,
        Tuesday,
        Wednesday,
        Thursday,
        Friday,
        Saturday,
        Sunday
    }
}

c#9新语法

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

namespace SharpGrammarInfo.SharpNine
{
    /// <summary>
    /// C#9
    /// </summary>
    public class SharpNineInfo
    {

        public static void Show()
        {
            //记录
            {
                FooInfo fooInfo = new FooInfo()
                {
                    PropA = "张三",
                    PropB = "李四"
                };
                fooInfo.PropA = "张三++";
                fooInfo.PropB = "张三++";
                var PropA = fooInfo.PropA;
                var PropB = fooInfo.PropB;

                ///为了满足，在一段程序执行过程中，有部分数据只是作为一个记录，
                ///一旦赋值不能修改；
                //FooInfo001 fooInfo001 = new FooInfo001()
                //{
                //    PropA = "123456",
                //    PropB = "456789"
                //};
                //fooInfo001.PropA = "5678";
                //fooInfo001.PropB = "测试";


                FooInfo002 fooInfo002 = new FooInfo002("5678", "测试");
                string propa = fooInfo002.PropA;
                string propb = fooInfo002.PropB;

                //fooInfo002.PropA = "";

                //Init是针对于类内部的字段而言；
                FooInfo003 fooInfo003 = new FooInfo003()
                {
                    PropA = "FooInfo003",
                    PropB = "FooInfo003_1"
                };
                //fooInfo003.PropA = "";//报错
                //fooInfo003.PropB = "";//报错
                string propa3 = fooInfo003.PropA;
                string propb3 = fooInfo003.PropB;


                //Record关键字 
                Person person = new Person("朝夕", "教育"); 
                string firstName = person.FirstName;
                string lastName = person.LastName;




                //person.LastName = "培训";//报错 
                var otherPerson = person with { FirstName = "武汉朝夕" };
                Console.WriteLine(object.ReferenceEquals(person, otherPerson));


                Teacher teacher = new Teacher("朝夕", "教育", "科技有限公司");
                string firstname1 = teacher.FirstName;

                //teacher.FirstName = "";//报错了

                var teachernew = teacher with { };  //with 表达式指示编译器创建记录的副本 
                Console.WriteLine(object.ReferenceEquals(teacher, teachernew));

            };


            #region 顶级语句
            //见控制台输出语句
            #endregion


            //简化
            #region 对象声明
            { 
                //FooInfo foo = new FooInfo(); 
                FooInfo fooInfo1 = new();  //语法糖
                FooInfo fooInfo2 = new() { PropA = "123", PropB = "234" };
            }
            #endregion

            #region 方法调用
            {
                var result = ForecastFor(1, "Richard", new());
            }
            #endregion


            #region 静态修饰  
            {
                Func<int> func = static () => 1;
            }

            #endregion


            #region 模式匹配
            char a = 'A';
            bool bResult = a.IsLetterNew();
            #endregion


            #region 为空判断 
            string name = "Ricahrd";

            if (string.IsNullOrWhiteSpace(name))
            {

            }

            if (name is not null)
            {

            }
            #endregion


            #region 协变式返回值（Covariant returns）
            {

            }
            #endregion

            #region nint
            {
                // 原生大小的数字类型
                //这次引入一组新类型（nint，nuint，nfloat等）'n'表示native(原生),该特性允许声明一个32位或64位的数据类型,这取决于操作系统的平台类型。
                nint nativeInt = 55; //在32位主机中编译时，需要4个字节。    
                nint nativeInt1 = 55; //使用x64编译设置在64位主机中编译时需要8个字节。
                //uint;
            }
            #endregion

            #region Lambda 参数弃元 
            {
                // C# 9 之前
                Func<int, int, int> zero = (a, b) => 0;
                Func<int, int, int> func = delegate (int a, int b) { return 0; };
            }

            // C# 9
            {
                Func<int, int, int> zero = (_, _) => 0;
                Func<int, int, int> func = delegate (int _, int _) { return 0; };
            }

            //在 C# 9 之前，即便不使用的 Lambda 参数也需要给它命名。C# 9 支持弃元参数一方面简化了命名，
            //另一方面也节省了内存分配。更重要的是它使得编程的意图更明确，让人一看就知道这个参数是不用的，
            //增强了代码的可读性和可维护性。
            #endregion

        }


        private static SharpNineInfo ForecastFor(int id, string name, FooInfo fooInfo)
        {
            return new();
        }


        private static Expression<Func<UserInfo, bool>> expression = u => u.Id > 0;


    }


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

    }
}