一.out的形参变量无需再提前声明
befor：
string input = "3"; int numericResult; if (int.TryParse(input, out numericResult)) Console.WriteLine(numericResult); else Console.WriteLine("Could not parse input"); after：
string input = "3"; if (int.TryParse(input, out var numericResult)) Console.WriteLine(numericResult); else Console.WriteLine("Could not parse input"); 二.扩展了元组（Tuple的使用，需要Nuget引用 System.ValueTuple）
1.命名的改进：
①.无命名，仅能通过无意义的Item1,Item2进行访问：
var letters = ("a", "b"); Console.WriteLine($"Value is {letters.Item1} and {letters.Item2>}"); befor:
(string first, string second) letters = ("a", "b"); Console.WriteLine($"Value is {letters.first} and {letters.second}"); after:
var letters = (first: "a",second: "b"); Console.WriteLine($"Value is {letters.first} and {letters.second}"); 混合型命名：（会有一个编译警告，仅以左侧命名为准）
(string leftFirst,string leftSecond) letters = (first: "a", second: "b"); Console.WriteLine($"Value is {letters.leftFirst} and {letters.leftSecond}"); 2.函数返回元组、对象转元组
static void Main(string[] args) { var p = GetData(); Console.WriteLine($"value is {p.name} and {p.age}"); } private static (string name,int age) GetData() { return ("han mei", 23); } 三.Local function (本地函数)
static void Main(string[] args) { var v = Fibonacci(3); Console.WriteLine($"value is {v}"); } private static int Fibonacci(int x) { if (x < 0) throw new ArgumentException("Less negativity please!", nameof(x)); return Fib(x).current; (int current, int previous) Fib(int i) { if (i == 0) return (1, 0); var (p, pp) = Fib(i - 1); return (p + pp, p); } } 四.Literal improments(字义改进)
1.数字间可以增加分隔符：_ (增加可读性)
2.可以直接声明二进制 （使用二进制的场景更方便，比如掩码、用位进行权限设置等）
var d = 123_456; var x = 0xAB_CD_EF; var b = 0b1010_1011_1100_1101_1110_1111;
五.Ref returns and locals (返回引用[返回的变量可以是一个引用])
static void Main(string[] args) { int[] array = { 1, 15, -39, 0, 7, 14, -12 }; ref int place = ref Find(7, array); // aliases 7's place in the array place = 9; // replaces 7 with 9 in the array Console.WriteLine(array[4]); // prints 9 } private static ref int Find(int number, int[] numbers) { for (int i = 0; i < numbers.Length; i++) { if (numbers[i] == number) { return ref numbers[i]; // return the storage location, not the value } } throw new IndexOutOfRangeException($"{nameof(number)} not found"); } 六.More expression bodied members(更多的表达式体的成员)
支持更多的成员使用表达式体，加入了访问器、构造函数、析构函数使用表达式体
class Person { private static ConcurrentDictionary<int, string> names = new ConcurrentDictionary<int, string>(); private int id = 123; public Person(string name) => names.TryAdd(id, name); // constructors ~Person() => names.TryRemove(id, out var v); // destructors public string Name { get => names[id]; // getters set => names[id] = value; // setters } } 七.Throw expressions(抛出表达式)
将异常直接作为表达式抛出，不管是用表达式体时，还是普通的return 时可以直接作为一个表达式来写。
class Person { public string Name { get; } public Person(string name) => Name = name ?? throw new ArgumentNullException(name); public string GetFirstName() { var parts = Name.Split(' '); return (parts.Length > 0) ? parts[0] : throw new InvalidOperationException("No name!"); } public string GetLastName() => throw new NotImplementedException(); } 八.Generalized async return types(全面异步返回类型)
需要Nuget引用System.Threading.Tasks.Extensions。异步时能返回更多的类型。
public async ValueTask<int> Func() { await Task.Delay(100); return 5; } 九.Pattern matching（模式匹配）
1. is 表达式 ，判断类型的同时创建变量
public static int DiceSum2(IEnumerable<object> values) { var sum = 0; foreach(var item in values) { if (item is int val) sum += val; else if (item is IEnumerable<object> subList) sum += DiceSum2(subList); } return sum; } 2. switch 表达式，允许case后的条件判断的同时创建变量
public static int DiceSum5(IEnumerable<object> values) { var sum = 0; foreach (var item in values) { switch (item) { case 0: break; case int val: sum += val; break; case PercentileDie die: sum += die.Multiplier * die.Value; break; case IEnumerable<object> subList when subList.Any(): sum += DiceSum5(subList); break; case IEnumerable<object> subList: break; case null: break; default: throw new InvalidOperationException("unknown item type"); } } return sum; } 参考内容：https://www.cnblogs.com/dev2007/p/6526261.html