13 个 C# 10 特性
<img style="width: 620px; margin-top: 20px" src="https://blog-1259586045.cos.ap-shanghai.myqcloud.com/sUQ1PGGoW.jpg"><blockquote>
<p>原文链接：https://blog.okyrylchuk.dev<br>
原文作者：Oleg Kyrylchuk<br>
译: 等天黑</p>
</blockquote>
<h2 id="常量的内插字符串">常量的内插字符串</h2>
<p>C# 10 允许使用在常量字符串初始化中使用插值,如下</p>
<pre><code class="language-csharp">const string name = "Oleg";
const string greeting = $"Hello, {name}.";
Console.WriteLine(greeting);
// Output: Hello, Oleg.
</code></pre>
<h2 id="扩展属性模式">扩展属性模式</h2>
<p>从 C# 10 开始，您可以在适当的模式中引用嵌套的属性或字段， 属性模式变得更具可读性并且需要更少的大括号。</p>
<pre><code class="language-csharp">Person person = new()
{
Name = "Oleg",
Location = new() { Country = "PL" }
};
if (person is { Name: "Oleg", Location.Country: "PL" })
{
Console.WriteLine("It's me!");
}
class Person
{
public string Name { get; set; }
public Location Location { get; set; }
}
class Location
{
public string Country { get; set; }
}
</code></pre>
<p>如果Location为null，则不会匹配模式并返回false。</p>
<h2 id="文件范围的命名空间">文件范围的命名空间</h2>
<p>C# 10 引入了一种新的命名空间声明方式 - 文件范围的命名空间，减少一个大括号，代码结构更简洁。</p>
<pre><code class="language-csharp">namespace FileScopedNamespace;
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Hello World!");
}
}
</code></pre>
<h2 id="全局-using">全局 Using</h2>
<p>一次引用，全局通用</p>
<pre><code class="language-csharp">global using System;
global using System.Collections.Generic;
global using System.Linq;
global using System.Threading.Tasks;
List<int> list = new() { 1, 2, 3, 4 };
int sum = list.Sum();
Console.WriteLine(sum);
await Task.Delay(1000);
</code></pre>
<h2 id="同一个解构中的赋值和声明">同一个解构中的赋值和声明</h2>
<p>C# 10 可以在同一个解构中进行赋值和声明。</p>
<pre><code class="language-csharp">var rgb = (255, 100, 30);
// Initialization & assignment
int r;
(r, int g, int b) = rgb;
Console.WriteLine($"RGB: {r}, {g}, {b}");
// Output: RGB: 255, 100, 30
</code></pre>
<h2 id="record-类型重写-tostring-时支持密封">Record 类型重写 ToString() 时支持密封</h2>
<pre><code class="language-csharp">Product product = new() { Name = "Bread" };
Console.WriteLine(product.ToString());
// Output: Bread
public record Product
{
public string Name { get; init; }
public sealed override string ToString()
{
return Name;
}
}
</code></pre>
<h2 id="record-struct">Record Struct</h2>
<p>C# 10 支持 record struct</p>
<pre><code class="language-csharp">Person me = new() { FirstName = "Oleg", LastName = "Kyrylchuk" };
Console.WriteLine(me);
// Output: Person { FirstName = Oleg, LastName = Kyrylchuk }
Person otherPerson = me with { FirstName = "John" };
Console.WriteLine(otherPerson);
// Output: Person { FirstName = John, LastName = Kyrylchuk }
Person anotherMe = new() { FirstName = "Oleg", LastName = "Kyrylchuk" };
C onsole.WriteLine(me == anotherMe);
// Output: True
record struct Person
{
public string FirstName { get; init; }
public string LastName { get; init; }
}
record struct Product(string Name, decimal Price);
</code></pre>
<h2 id="struct-字段支持初始化">Struct 字段支持初始化</h2>
<pre><code class="language-csharp">using System;
Person person = new() { Name = "Oleg" };
Console.WriteLine(person.Id + " " + person.Name);
// Output: 0cc6caac-d061-4f46-9301-c7cc2a012e47 Oleg
struct Person
{
public Guid Id { get; init; } = Guid.NewGuid();
public string Name { get; set; }
}
</code></pre>
<h2 id="lambda-表达式的-attributes-支持">Lambda 表达式的 Attributes 支持</h2>
<p>C# 9 支持本地函数的 Attributes, C# 10 添加了 Lambda 表达式的 Attributes 支持。</p>
<pre><code class="language-csharp">Action a = () => { };
Action<int> b = (x) => { };
Action<int> c = ( x) => { };
class MyAttribute : Attribute
{ }
</code></pre>
<h2 id="lambda-中的显式返回类型">Lambda 中的显式返回类型</h2>
<pre><code class="language-csharp">Test<int>();
var l1 = string () => string.Empty;
var l2 = int () => 0;
var l3 = static void () => { };
void Test<T>()
{
var l4 = T () => default;
}
</code></pre>
<h2 id="应用于方法的-asyncmethodbuilder--特性">应用于方法的 AsyncMethodBuilder特性</h2>
<p>从 C# 7 开始，您只能将<em>AsyncMethodBuilder</em> 特性应用于类型, 在 C# 10 中，您还可以将该特性应用于单个方法。</p>
<pre><code class="language-csharp">using System.Runtime.CompilerServices;
class Example
{
public void ExampleMethod()
{
}
}
</code></pre>
<h2 id="结构体中的表达式">结构体中的表达式</h2>
<p>C# 10 支持 将 with 表达式和 struct 一起使用</p>
<pre><code class="language-csharp">Product potato = new() { Name = "Potato", Category = "Vegetable" };
Console.WriteLine($"{potato.Name} {potato.Category}");
// Output: Potato Vegetable
Product tomato = potato with { Name = "Tomato" };
Console.WriteLine($"{tomato.Name} {tomato.Category}");
// Output: Tomato Vegetable
struct Product
{
public string Name { get; set; }
public string Category { get; set; }
}
</code></pre>
<h2 id="匿名类型中的表达式">匿名类型中的表达式</h2>
<p>C# 10 支持 将 with 表达式和匿名类型一起使用</p>
<pre><code class="language-csharp">var potato = new { Name = "Potato", Category = "Vegetable" };
Console.WriteLine($"{potato.Name} {potato.Category}");
// Output: Potato Vegetable
var onion = potato with { Name = "Onion" };
Console.WriteLine($"{onion.Name} {onion.Category}");
// Output: Onion Vegetable
</code></pre>
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来源：https://www.cnblogs.com/myshowtime/p/15747663.html
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