Shulou(Shulou.com)06/03 Report--

This article mainly introduces what are the new features in C#7.0. The introduction in this article is very detailed and has certain reference value. Interested friends must read it!

preface

Microsoft yesterday released the new VS 2017.. There is a lot more to it. . NET New Version ASP.NET New Version... Wait a minute. Too many.. It's really hard.

In fact, December 2016 has been announced in C#7.0 new features bar, although it came out early, but we do not support this IDE ah..

However, in yesterday's VS2017 has been perfectly able to support the use.

E text good, move to the official introduction address: https://docs.microsoft.com/zh-cn/dotnet/articles/csharp/csharp-7

Let's start with the syntax:

1.out-variables(Out variables)

2. Tuples (tuple)

3. Pattern Matching

4. ref locations and returns

5. Local Functions

6. More expression-bodied members

7. throw Expressions

8. Generalized asynchronous return types

9. Numeric literal syntax improvements

text

1. out-variables(Out variables)

In the past, when we used the out variable, we needed to declare it externally before we could pass it into the method, similar to the following:

string ddd = ""; //declare variables ccc.StringOut(out ddd);Console.WriteLine(ddd);

In C#7.0 we can declare it directly with the parameter passing without declaring it, as follows:

StringOut(out string ddd); //while passing declaration Console.WriteLine(ddd);Console.ReadLine();

2. Tuples (tuple)

In. NET 4.0, Microsoft gave us a solution for multiple return values called tuples, something like this:

static void Main(string[] args) { var data = GetFullName(); Console.WriteLine(data.Item1); Console.WriteLine(data.Item2); Console.WriteLine(data.Item3); Console.ReadLine();}static Tuple GetFullName() { return new Tuple("a", "b", "c");}

The above code shows a method that returns a tuple of three strings, but when we get the value, our heart explodes when we use it,Item1,Item2,Item3 is what the hell, although it meets our requirements, but it is not elegant.

So, in C#7.0, Microsoft provides a more elegant solution:(Note: you need to reference System.ValueTuple via nuget) as follows:

static void Main(string[] args) { var data=GetFullName(); Console.WriteLine(data.a); //Get values with names Console.WriteLine(data.b); Console.WriteLine (data.c); Console.ReadLine(); }/Method defines multiple return values and names private static (string a,string b,string c) GetFullName() { return ("a","b","c"); }

Destruct tuples, sometimes we don't want to get var anonymously, so how do we get abc? We can do the following:

static void Main(string[] args) { //defineddestruct (string a, string b, string c) = GetFullName(); Console.WriteLine(a); Console. WriteLine(b); Console. WriteLine(c); Console.ReadLine(); } private static (string a,string b,string c) GetFullName() { return ("a","b","c"); }

3. Pattern Matching

In C#7.0, matching mode is introduced, starting with an old chestnut. An object type, we want to determine whether it is int if it is int we add 10, and then output, we need the following:

object a = 1;if (a is int) //is { int b = (int)a; //split int d = b+10; //add 10 Console.WriteLine(d); //output}

So in C#7.0, the first is a small extension to is, we just need to write this:

object a = 1;if (a is int c) //here, after judging int, it is directly assigned to c{ int d = c + 10; Console.WriteLine(d);}

Is that convenient? Especially comrades who often use reflexes..

So the question is, which excavator technology is strong?! (cough, pui kidding)

Actually, what if there are multiple types to match? How many if else? Of course, there is no problem, but Microsoft Dad also provides a new way to play switch, let's take a look, as follows:

We define an Add method that takes Object as an argument and returns a dynamic type.

static dynamic Add(object a) { dynamic data; switch (a) { case int b: data=b++; break; case string c: data= c + "aaa"; break; default: data = null; break; } return data; }

Run the following, passing in int type:

object a = 1;var data= Add(a);Console.WriteLine(data.GetType());Console.WriteLine(data);

The output is as follows:

We pass in parameters of type String, the code and output are as follows:

object a = "bbbb";var data= Add(a);Console.WriteLine(data.GetType());Console.WriteLine(data);

With the above code, we can appreciate how smooth and powerful switch's new gameplay is.

Case When filtering matching patterns

Some gay friends are gonna ask. Now that we can match types in Switch, can we filter the values? The answer, of course, is yes.

We change the Switch code above as follows:

switch (a) { case int b when b

< 0: data = b + 100; break; case int b: data=b++; break; case string c: data= c + "aaa"; break; default: data = null; break; } 在传入-1试试,看结果如下: 4.ref locals and returns(局部变量和引用返回) 已经补上,请移步：C# 7.0之ref locals and returns（局部变量和引用返回） 5.Local Functions (局部函数) 嗯,这个就有点颠覆..大家都知道,局部变量是指:只在特定过程或函数中可以访问的变量。 那这个局部函数,顾名思义:只在特定的函数中可以访问的函数(妈蛋 好绕口) 使用方法如下: public static void DoSomeing() { //调用Dosmeing2 int data = Dosmeing2(100, 200); Console.WriteLine(data); //定义局部函数,Dosmeing2. int Dosmeing2(int a, int b) { return a + b; } } 呃,解释下来 大概就是在DoSomeing中定义了一个DoSomeing2的方法,..在前面调用了一下. (注:值得一提的是局部函数定义在方法的任何位置,都可以在方法内被调用,不用遵循逐行解析的方式) 6.More expression-bodied members(更多的函数成员的表达式体) C#6.0中,提供了对于只有一条语句的方法体可以简写成表达式。 如下: public void CreateCaCheContext() =>

new CaCheContext(); //Equivalent to public void CreateCaCheContext() { new CaCheContext(); }

However, it doesn't support constructors, destructors, and attribute accessors, so C#7.0 does. The code is as follows:

//constructor expression public CaCheContext(string label) => this.Label = label;//destructor expression ~CaCheContext() => Console.Error.WriteLine("Finalized! ");private string label;// Get/Set property accessor expression writing public string Label{ get => label; set => this.label = value ?? "Default label";}

7. throw Expressions

Before C#7.0, if we wanted to determine whether a string was null and throw the exception if null, we would write:

public string IsNull() { string a = null; if (a == null) { throw new Exception("Exception! "); } return a; }

So, we're very inconvenient, especially in ternary expressions or non-null expressions, we can't throw out this exception, we need to write an if statement.

So in C#7.0, we can do this:

public string IsNull() { string a = null; return a ?? throw new Exception("Exception! "); }

8. Generalized asynchronous return types

Um, this, how should I put it? Actually, I don't use asynchronous very much, so I don't have a deep understanding of this feeling, but I still think it should be useful under certain circumstances.

I directly translated the official original, the example code is also the official original.

Asynchronous methods must return void, Task or Task, this time adding a new ValueTask to prevent asynchronous execution from assigning Task in situations where the result is already available while waiting. For asynchronous scenarios where buffering is designed in many examples, this can significantly reduce the number of allocations and significantly improve performance.

The main meaning of the official example is: a data, in the case of cached, you can use ValueTask to return asynchronous or synchronous 2 schemes

public class CaCheContext { public ValueTask CachedFunc() { return (cache) ? new ValueTask(cacheResult) : new ValueTask(loadCache()); } private bool cache = false; private int cacheResult; private async Task loadCache() { // simulate async work: await Task.Delay(5000); cache = true; cacheResult = 100; return cacheResult; } }

The code and result of the call are as follows:

//main method cannot be decorated with async, so delegate is used. static void Main(string[] args) { Action act = async () => { CaCheContext cc = new CaCheContext(); int data = await cc.CachedFunc(); Console.WriteLine(data); int data2 = await cc.CachedFunc(); Console.WriteLine(data2); }; //invoke delegate act(); Console.Read(); }

The code above, we called 2 times in a row, the first time, waiting for 5 seconds to appear results. The second time, there was no waiting for direct results and the expected results were consistent.

9. Numeric literal syntax improvements

This is the first time. To look good.

In C#7.0, the divisor "_" is allowed in numbers. to improve readability, for example:

int a = 123_456; int b = 0xAB_CD_EF; int c = 123456; int d = 0xABCDEF; Console. WriteLine(a==c); Console.WriteLine(b==d);

Of course, since it's a numeric delimiter, decimal, float, and double can all be split in this way.

That's all for "What's new in C#7.0", thanks for reading! Hope to share the content to help everyone, more relevant knowledge, welcome to pay attention to the industry information channel!

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