Những điểm mới trong C# 9

Thứ Sáu, 14/08/2020

Tram Ho

(1) Visual Studio

Cần sử dụng mới nhất bản xem trước Visual Studio, sửa lại tệp *.csproj thành

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span> Project</span> <span class="token attr-name">Sdk</span> <span class="token attr-value"><span class="token punctuation">=</span> <span class="token punctuation">"</span> Microsoft.NET.Sdk <span class="token punctuation">"</span></span> <span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span> PropertyGroup</span> <span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span> OutputType</span> <span class="token punctuation">&gt;</span></span> Exe <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span> OutputType</span> <span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span> TargetFramework</span> <span class="token punctuation">&gt;</span></span> net5.0 <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span> TargetFramework</span> <span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span> LangVersion</span> <span class="token punctuation">&gt;</span></span> 9.0 <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span> LangVersion</span> <span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span> PropertyGroup</span> <span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span> Project</span> <span class="token punctuation">&gt;</span></span>

< Project Sdk = " Microsoft.NET.Sdk " >

< PropertyGroup >

< OutputType > Exe </ OutputType >

< TargetFramework > net5.0 </ TargetFramework >

< LangVersion > 9.0 </ LangVersion >

</ PropertyGroup >

</ Project >

(2) Nhập mục tiêu tính năng

File Program.cs

Old method

<span class="token keyword">namespace</span> <span class="token namespace">csharp9 <span class="token punctuation">.</span> old1</span>
<span class="token punctuation">{</span>
    <span class="token keyword">class</span> <span class="token class-name">Program1Old</span>
    <span class="token punctuation">{</span>

        <span class="token return-type class-name"><span class="token keyword">void</span></span> <span class="token function">MyMethod</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
        <span class="token punctuation">{</span>
            <span class="token class-name">Person</span> person <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token constructor-invocation class-name">Person</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span> <span class="token comment">//&lt;-- Trong C# 8.</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">class</span> <span class="token class-name">Person</span>
    <span class="token punctuation">{</span>
        <span class="token keyword">public</span> <span class="token return-type class-name"><span class="token keyword">string</span></span> FirstName <span class="token punctuation">{</span> <span class="token keyword">get</span> <span class="token punctuation">;</span> <span class="token keyword">set</span> <span class="token punctuation">;</span> <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

<span class="token punctuation">}</span>

namespace csharp9 . old1

{

class Program1Old

{

void MyMethod ( )

{

Person person = new Person ( ) ; //<-- Trong C# 8.

}

class Person

{

public string FirstName { get ; set ; }

}

New Cú pháp

<span class="token keyword">namespace</span> <span class="token namespace">csharp9 <span class="token punctuation">.</span> new1</span>
<span class="token punctuation">{</span>

    <span class="token keyword">class</span> <span class="token class-name">ProgramNew</span>
    <span class="token punctuation">{</span>
        <span class="token return-type class-name"><span class="token keyword">void</span></span> <span class="token function">MyMethod</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
        <span class="token punctuation">{</span>
            <span class="token class-name">Person</span> person <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span> <span class="token comment">//&lt;-- Trong C# 9.</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">class</span> <span class="token class-name">Person</span>
    <span class="token punctuation">{</span>
        <span class="token keyword">public</span> <span class="token return-type class-name"><span class="token keyword">string</span></span> FirstName <span class="token punctuation">{</span> <span class="token keyword">get</span> <span class="token punctuation">;</span> <span class="token keyword">set</span> <span class="token punctuation">;</span> <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

<span class="token punctuation">}</span>

namespace csharp9 . new1

{

class ProgramNew

{

Person person = new ( ) ; //<-- Trong C# 9.

}

class Person

{

}

(3) Thuộc tính Init-only tính năng

Old way

<span class="token keyword">using</span> <span class="token namespace">System</span> <span class="token punctuation">;</span>

<span class="token keyword">namespace</span> <span class="token namespace">csharp9 <span class="token punctuation">.</span> old2</span>
<span class="token punctuation">{</span>

    <span class="token keyword">class</span> <span class="token class-name">Program2Old</span>
    <span class="token punctuation">{</span>
        <span class="token keyword">static</span> <span class="token return-type class-name"><span class="token keyword">void</span></span> <span class="token function">Main</span> <span class="token punctuation">(</span> <span class="token class-name"><span class="token keyword">string</span> <span class="token punctuation">[</span> <span class="token punctuation">]</span></span> args <span class="token punctuation">)</span>
        <span class="token punctuation">{</span>
            <span class="token class-name"><span class="token keyword">var</span></span> person <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token constructor-invocation class-name">Person</span> <span class="token punctuation">(</span> <span class="token string">"Nguyễn Văn A"</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>
            person <span class="token punctuation">.</span> Name <span class="token operator">=</span> <span class="token string">"xx"</span> <span class="token punctuation">;</span>
            Console <span class="token punctuation">.</span> <span class="token function">WriteLine</span> <span class="token punctuation">(</span> person <span class="token punctuation">.</span> Name <span class="token punctuation">)</span> <span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Person</span>
    <span class="token punctuation">{</span>
        <span class="token keyword">public</span> <span class="token function">Person</span> <span class="token punctuation">(</span> <span class="token class-name"><span class="token keyword">string</span></span> name <span class="token punctuation">)</span>
        <span class="token punctuation">{</span>
            <span class="token keyword">this</span> <span class="token punctuation">.</span> Name <span class="token operator">=</span> name <span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
        <span class="token keyword">public</span> <span class="token return-type class-name"><span class="token keyword">string</span></span> Name <span class="token punctuation">{</span> <span class="token keyword">get</span> <span class="token punctuation">;</span> <span class="token keyword">set</span> <span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token comment">// Trong C# 8.</span>
    <span class="token punctuation">}</span>

<span class="token punctuation">}</span>

using System ;

namespace csharp9 . old2

{

class Program2Old

{

static void Main ( string [ ] args )

{

var person = new Person ( "Nguyễn Văn A" ) ;

person . Name = "xx" ;

Console . WriteLine ( person . Name ) ;

}

public class Person

{

public Person ( string name )

{

this . Name = name ;

}

public string Name { get ; set ; } // Trong C# 8.

}

New Way in C # 9

<span class="token keyword">using</span> <span class="token namespace">System</span> <span class="token punctuation">;</span>

<span class="token keyword">namespace</span> <span class="token namespace">csharp9 <span class="token punctuation">.</span> new2</span>
<span class="token punctuation">{</span>
    <span class="token keyword">class</span> <span class="token class-name">Program</span>
    <span class="token punctuation">{</span>
        <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token return-type class-name"><span class="token keyword">void</span></span> <span class="token function">Main</span> <span class="token punctuation">(</span> <span class="token class-name"><span class="token keyword">string</span> <span class="token punctuation">[</span> <span class="token punctuation">]</span></span> args <span class="token punctuation">)</span>
        <span class="token punctuation">{</span>
            <span class="token class-name"><span class="token keyword">var</span></span> person <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token constructor-invocation class-name">Person</span> <span class="token punctuation">(</span> <span class="token string">"Tran Van B"</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>
            Console <span class="token punctuation">.</span> <span class="token function">WriteLine</span> <span class="token punctuation">(</span> person <span class="token punctuation">.</span> Name <span class="token punctuation">)</span> <span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Person</span>
    <span class="token punctuation">{</span>
        <span class="token keyword">public</span> <span class="token function">Person</span> <span class="token punctuation">(</span> <span class="token class-name"><span class="token keyword">string</span></span> name <span class="token punctuation">)</span>
        <span class="token punctuation">{</span>
            <span class="token keyword">this</span> <span class="token punctuation">.</span> Name <span class="token operator">=</span> name <span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
        <span class="token keyword">public</span> <span class="token return-type class-name"><span class="token keyword">string</span></span> Name <span class="token punctuation">{</span> <span class="token keyword">get</span> <span class="token punctuation">;</span> init <span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token comment">// Trong C# 9.</span>
    <span class="token punctuation">}</span>

<span class="token punctuation">}</span>

using System ;

namespace csharp9 . new2

{

class Program

{

public static void Main ( string [ ] args )

{

var person = new Person ( "Tran Van B" ) ;

}

public class Person

{

this . Name = name ;

}

public string Name { get ; init ; } // Trong C# 9.

}

(4) Keyword “is” and “and”

<span class="token keyword">using</span> <span class="token namespace">System</span> <span class="token punctuation">;</span>

<span class="token keyword">namespace</span> <span class="token namespace">csharp9 <span class="token punctuation">.</span> new3</span>
<span class="token punctuation">{</span>
    <span class="token keyword">class</span> <span class="token class-name">Program</span>
    <span class="token punctuation">{</span>
        <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token return-type class-name"><span class="token keyword">void</span></span> <span class="token function">Main</span> <span class="token punctuation">(</span> <span class="token class-name"><span class="token keyword">string</span> <span class="token punctuation">[</span> <span class="token punctuation">]</span></span> args <span class="token punctuation">)</span>
        <span class="token punctuation">{</span>
            <span class="token class-name"><span class="token keyword">int</span></span> <span class="token keyword">value</span> <span class="token operator">=</span> <span class="token number">42</span> <span class="token punctuation">;</span>

            <span class="token keyword">switch</span> <span class="token punctuation">(</span> <span class="token keyword">value</span> <span class="token punctuation">)</span>
            <span class="token punctuation">{</span>
                <span class="token keyword">case</span> <span class="token operator">&lt;=</span> <span class="token number">0</span> <span class="token punctuation">:</span>
                    Console <span class="token punctuation">.</span> <span class="token function">WriteLine</span> <span class="token punctuation">(</span> <span class="token string">"Less than or equal to 0"</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>
                    <span class="token keyword">break</span> <span class="token punctuation">;</span>
                <span class="token keyword">case</span> <span class="token operator">&gt;</span> <span class="token number">0</span> and <span class="token operator">&lt;=</span> <span class="token number">10</span> <span class="token punctuation">:</span>
                    Console <span class="token punctuation">.</span> <span class="token function">WriteLine</span> <span class="token punctuation">(</span> <span class="token string">"More than 0 but less than or equal to 10"</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>
                    <span class="token keyword">break</span> <span class="token punctuation">;</span>
                <span class="token keyword">default</span> <span class="token punctuation">:</span>
                    Console <span class="token punctuation">.</span> <span class="token function">WriteLine</span> <span class="token punctuation">(</span> <span class="token string">"More than 10"</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>
                    <span class="token keyword">break</span> <span class="token punctuation">;</span>
            <span class="token punctuation">}</span>

            <span class="token class-name"><span class="token keyword">var</span></span> message <span class="token operator">=</span> <span class="token keyword">value</span> <span class="token keyword">switch</span>
            <span class="token punctuation">{</span>
                <span class="token operator">&lt;=</span> <span class="token number">0</span> <span class="token operator">=&gt;</span> <span class="token string">"Less than or equal to 0"</span> <span class="token punctuation">,</span>
                <span class="token operator">&gt;</span> <span class="token number">0</span> and <span class="token operator">&lt;=</span> <span class="token number">10</span> <span class="token operator">=&gt;</span> <span class="token string">"More than 0 but less than or equal to 10"</span> <span class="token punctuation">,</span>
                _ <span class="token operator">=&gt;</span> <span class="token string">"More than 10"</span>
            <span class="token punctuation">}</span> <span class="token punctuation">;</span>
            Console <span class="token punctuation">.</span> <span class="token function">WriteLine</span> <span class="token punctuation">(</span> message <span class="token punctuation">)</span> <span class="token punctuation">;</span>

            <span class="token keyword">if</span> <span class="token punctuation">(</span> <span class="token keyword">value</span> <span class="token operator">&gt;</span> <span class="token number">0</span> <span class="token operator">&amp;&amp;</span> <span class="token keyword">value</span> <span class="token operator">&lt;=</span> <span class="token number">10</span> <span class="token punctuation">)</span> <span class="token comment">// Trong C# 8.</span>
            <span class="token punctuation">{</span>
                Console <span class="token punctuation">.</span> <span class="token function">WriteLine</span> <span class="token punctuation">(</span> <span class="token string">"More than 0 but less than or equal to 10"</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>
            <span class="token punctuation">}</span>

            <span class="token keyword">if</span> <span class="token punctuation">(</span> <span class="token keyword">value</span> <span class="token keyword">is</span> <span class="token operator">&gt;</span> <span class="token number">0</span> and <span class="token operator">&lt;=</span> <span class="token number">10</span> <span class="token punctuation">)</span> <span class="token comment">// Trong C# 9.</span>
            <span class="token punctuation">{</span>
                Console <span class="token punctuation">.</span> <span class="token function">WriteLine</span> <span class="token punctuation">(</span> <span class="token string">"More than 0 but less than or equal to 10"</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

<span class="token punctuation">}</span>

using System ;

namespace csharp9 . new3

{

class Program

{

int value = 42 ;

switch ( value )

{

case <= 0 :

Console . WriteLine ( "Less than or equal to 0" ) ;

break ;

case > 0 and <= 10 :

Console . WriteLine ( "More than 0 but less than or equal to 10" ) ;

break ;

default :

Console . WriteLine ( "More than 10" ) ;

break ;

}

var message = value switch

{

<= 0 => "Less than or equal to 0" ,

> 0 and <= 10 => "More than 0 but less than or equal to 10" ,

_ => "More than 10"

} ;

Console . WriteLine ( message ) ;

if ( value > 0 && value <= 10 ) // Trong C# 8.

{

Console . WriteLine ( "More than 0 but less than or equal to 10" ) ;

}

if ( value is > 0 and <= 10 ) // Trong C# 9.

{

Console . WriteLine ( "More than 0 but less than or equal to 10" ) ;

}

(5) Đối tượng ghi tính năng

<span class="token keyword">using</span> <span class="token namespace">System</span> <span class="token punctuation">;</span>

<span class="token keyword">namespace</span> <span class="token namespace">csharp9</span>
<span class="token punctuation">{</span>
    <span class="token keyword">class</span> <span class="token class-name">RecordObject</span>
    <span class="token punctuation">{</span>
        <span class="token keyword">static</span> <span class="token return-type class-name"><span class="token keyword">void</span></span> <span class="token function">Main</span> <span class="token punctuation">(</span> <span class="token class-name"><span class="token keyword">string</span> <span class="token punctuation">[</span> <span class="token punctuation">]</span></span> args <span class="token punctuation">)</span>
        <span class="token punctuation">{</span>
            <span class="token class-name"><span class="token keyword">var</span></span> book <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token constructor-invocation class-name">Book</span> <span class="token punctuation">{</span> Title <span class="token operator">=</span> <span class="token string">"Chí Phèo"</span> <span class="token punctuation">,</span> Author <span class="token operator">=</span> <span class="token string">"Nam Cao"</span> <span class="token punctuation">,</span> ISBN <span class="token operator">=</span> <span class="token string">"8935092514741"</span> <span class="token punctuation">}</span> <span class="token punctuation">;</span>
            <span class="token class-name"><span class="token keyword">var</span></span> newBook <span class="token operator">=</span> <span class="token return-type class-name">book</span> with <span class="token punctuation">{</span> Title <span class="token operator">=</span> <span class="token string">"Đôi lứa xứng đôi"</span> <span class="token punctuation">}</span> <span class="token punctuation">;</span> <span class="token comment">// Trong C# 9. Record Object.</span>
            Console <span class="token punctuation">.</span> OutputEncoding <span class="token operator">=</span> System <span class="token punctuation">.</span> Text <span class="token punctuation">.</span> Encoding <span class="token punctuation">.</span> UTF8 <span class="token punctuation">;</span>
            Console <span class="token punctuation">.</span> <span class="token function">WriteLine</span> <span class="token punctuation">(</span> newBook <span class="token punctuation">.</span> Title <span class="token punctuation">)</span> <span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">public</span> <span class="token return-type class-name">record</span> Book
    <span class="token punctuation">{</span>
        <span class="token keyword">public</span> <span class="token return-type class-name"><span class="token keyword">string</span></span> Title <span class="token punctuation">{</span> <span class="token keyword">get</span> <span class="token punctuation">;</span> init <span class="token punctuation">;</span> <span class="token punctuation">}</span>
        <span class="token keyword">public</span> <span class="token return-type class-name"><span class="token keyword">string</span></span> Author <span class="token punctuation">{</span> <span class="token keyword">get</span> <span class="token punctuation">;</span> init <span class="token punctuation">;</span> <span class="token punctuation">}</span>
        <span class="token keyword">public</span> <span class="token return-type class-name"><span class="token keyword">string</span></span> ISBN <span class="token punctuation">{</span> <span class="token keyword">get</span> <span class="token punctuation">;</span> init <span class="token punctuation">;</span> <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

<span class="token punctuation">}</span>

using System ;

namespace csharp9

{

class RecordObject

{

var book = new Book { Title = "Chí Phèo" , Author = "Nam Cao" , ISBN = "8935092514741" } ;

var newBook = book with { Title = "Đôi lứa xứng đôi" } ; // Trong C# 9. Record Object.

Console . OutputEncoding = System . Text . Encoding . UTF8 ;

Console . WriteLine ( newBook . Title ) ;

}

public record Book

{

public string Title { get ; init ; }

public string Author { get ; init ; }

public string ISBN { get ; init ; }

}

Mã nguồn: https://github.com/donhuvy/csharp9.git

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