C# 7.0

Posted AwuAwu

tags:

篇首语:本文由小常识网(cha138.com)小编为大家整理,主要介绍了C# 7.0相关的知识,希望对你有一定的参考价值。

visual studio 2017安装完后,马上全面体验下C# 7.0。

  • out variables (out变量)

out的形参变量无需再提前声明

之前:

            string input = "3";
            int numericResult;
            if (int.TryParse(input, out numericResult))
                Console.WriteLine(numericResult);
            else
                Console.WriteLine("Could not parse input");

 现在:

            string input = "3";
            if (int.TryParse(input, out var numericResult))
                Console.WriteLine(numericResult);
            else
                Console.WriteLine("Could not parse input");

 

  • Tuples (元组)

扩展了元组(Tuple的使用,需要Nuget引用 System.ValueTuple)

1.命名的改进:

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>}");

 以前版本的命名:

            (string first, string second) letters = ("a", "b");
            Console.WriteLine($"Value is {letters.first} and {letters.second}");

 现在的命名:

            var letters = (first: "a",second: "b");
            Console.WriteLine($"Value is {letters.first} and {letters.second}");

 现在混合型命名:(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

示例1:

        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);
        }

示例2:(注意类中应实现Deconstruct用于元组的转换)

 class Program
    {
        static void Main(string[] args)
        {
            var p = new Point(1.1, 2.1);
            (double first, double second) = p;
            Console.WriteLine($"value is {first} and {second}");
        }

    }

    public class Point
    {
        public Point(double x, double y)
        {
            this.X = x;
            this.Y = y;
        }

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

        public void Deconstruct(out double x, out double y)
        {
            x = this.X;
            y = this.Y;
        }
    }
  • Local function (本地函数)

可以在函数内部声明函数

示例:

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);
            }
        }

  

  • 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)

示例:

var d = 123_456;
var x = 0xAB_CD_EF;
var b = 0b1010_1011_1100_1101_1110_1111;
  • Ref returns and locals (返回引用)

返回的变量可以是一个引用。

示例:

        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");
        }
  • 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

示例:

    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
        }
    }
  • 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。

示例:(可以看到,很方便的直接进行值判断然后抛出异常)

    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();
    }
  • 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。

示例:

        public async ValueTask<int> Func()
        {
            await Task.Delay(100);
            return 5;
        }
  • Pattern matching(模式匹配)

1. is 表达式 ,判断类型的同时创建变量

示例:

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

示例:

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://docs.microsoft.com/en-us/dotnet/articles/csharp/csharp-7

以上是关于C# 7.0的主要内容,如果未能解决你的问题,请参考以下文章

C# 7.0 语言新特性

Nest Client c# 7.0 用于弹性搜索删除别名

从命令行编译新的 C# 版本(C# 7.0 更高版本)

C# 最有用的(自定义)代码片段是啥? [关闭]

c#代码片段快速构建代码

此 Canon SDK C++ 代码片段的等效 C# 代码是啥?