C# 9.0 支持 Visual Studio 2019 中的顶级程序

本文介绍了C# 9.0 支持 Visual Studio 2019 中的顶级程序的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

随着 C# 9.0 和 .NET 5 的到来，引入了一项称为顶级程序"的新功能.

With the coming of C# 9.0 and .NET 5 a new feature is getting introduced called "Top-level programs".

此功能无需将代码包装在通常的命名空间/类/Main 方法中，从而消除了创建简单 C# 应用程序所需的大量样板代码，如欢迎来到 C# 9.0 博客

This functionality takes away a lot of the boilerplate code necessary to create a simple C# application by not having to wrap your code in the usual namespace/class/Main method, as explained in the Welcome to C# 9.0 blog

创建一个简单的Hello World"应用程序唯一需要的顶级程序代码如下(摘自博客)

To create a simple "Hello World" application the only required code for a Top-level program is the following (taken from the blog)

using System;

Console.WriteLine("Hello World!");

为了试用此功能，我安装了在 Visual Studio 2019 (v16.6.5) 中运行的最新 .NET 5 预览包 (5.0.100-preview.6.20318.15) 并创建了以下正常"版本:从 VS 编译和运行的项目:

To try out this feature I have installed the latest .NET 5 preview package (5.0.100-preview.6.20318.15) running in Visual Studio 2019 (v16.6.5) and created the following "normal" project which compiles and runs from wihtin VS:

using System;

namespace TestProgram
{
    class Test
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello world!");
            var fooBar = "Foo" + "bar";
            Console.WriteLine(fooBar);
            Console.ReadLine();
        }
    }
}

为了测试顶级程序，看看可以(不)做什么，我去掉了命名空间、类定义和 Main 方法:

To test out the Top-level program and see what could(n't) be done with it I got rid of the namespace, class definition and Main method:

using System;

Console.WriteLine("Hello world!"); // 1
var fooBar = "Foo" + "bar"; // 2
Console.WriteLine(fooBar); // 3
Console.ReadLine(); // 3

现在应该是有效的语法.这是项目中唯一的文件，据我所知，它符合该博客中提到的所有其他标准:

Which should now be valid syntax. This is the only file in the project and to my knowledge it conforms to all other criteria mentioned in that blog:

允许任何语句.程序必须出现在 using 之后，文件中的任何类型或命名空间声明之前，并且您只能在一个文件中执行此操作，就像今天只能有一个 Main 方法一样.

但是在实践中 VS 强调了所有错误，这些错误阻止我从 VS 中编译为发布或调试.

However in practise VS underlines everything with the errors preventing me from compiling as either release or debug from within VS.

(1) 命名空间不能直接包含字段或方法等成员
(2) 上下文关键字var"只能出现在局部变量声明或脚本代码中
(3)名称Console.WriteLine(/ReadLine)在当前上下文中不存在

人们希望在 VS pre-.NET 5 中看到什么，但是 .NET 5 肯定已启用，语言预览功能也是如此.如 .csproj 所示:

Which is what one would expect to see in VS pre-.NET 5, however .NET 5 is surely enabled, and so are language preview functions. As seen in the .csproj:

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

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <LangVersion>preview</LangVersion>
    <TargetFramework>net5.0</TargetFramework>
  </PropertyGroup>

</Project>

对我来说奇怪的是，当我尝试使用 dotnet build 从 CLI 编译时，程序会编译，并且可执行文件运行完美.

To me the odd thing is that when I try to compile from the CLI using dotnet build the program compiles, and the executable runs flawlessly.

Visual Studio 是否有错，它尚不支持此语法，还是我必须在某处启用某些功能才能使顶级程序成为一件事?

Is Visual Studio at fault here that it does not support this syntax yet, or do I have to enable something somewhere to make Top-level programs a thing?

中的顶级程序

C# 9.0 支持 Visual Studio 2019 中的顶级程序

问题描述

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