C# 7.0特性

时间:2021-11-27 19:24:13

一.out的形参变量无需再提前声明

befor:

string input = "";
int numericResult;
if (int.TryParse(input, out numericResult))
Console.WriteLine(numericResult);
else
Console.WriteLine("Could not parse input");

after:

string input = "";
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", );
}

三.Local function (本地函数)

static void Main(string[] args)
{
var v = Fibonacci();
Console.WriteLine($"value is {v}");
} private static int Fibonacci(int x)
{
if (x < ) throw new ArgumentException("Less negativity please!", nameof(x));
return Fib(x).current; (int current, int previous) Fib(int i)
{
if (i == ) return (, );
var (p, pp) = Fib(i - );
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 = { , , -, , , , - };
ref int place = ref Find(, array); // aliases 7's place in the array
place = ; // replaces 7 with 9 in the array
Console.WriteLine(array[]); // prints 9
} private static ref int Find(int number, int[] numbers)
{
for (int i = ; 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 = ; 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 > ) ? parts[] : 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();
return ;
}

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 = ;
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 = ;
foreach (var item in values)
{
switch (item)
{
case :
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