与过去相比，Microsoft希望将C#语言版本与框架版本更紧密地联系在一起.他们真的只希望您将C#8与.NET Core 3.x和.NET Standard 2.1项目一起使用，这意味着使用Visual Studio2019.我对

Going forward, Microsoft want to tie C# language versions more closely to framework versions than they have in the past. They really only want you to be using C# 8 with .NET Core 3.x and .NET Standard 2.1 projects, and that means using Visual Studio 2019. My answer to Does C# 8 support the .NET Framework? has all the gory details.

但是，如果您真的想现在可以通过使用将C#7带入Visual Studio 2015的相同技巧:安装最新版本的将Microsoft.Net.Compilers Nuget程序包放入项目.它可以工作，但是VS 2017当然不了解C#8语法，因此看起来不太漂亮.这是一个截图，显示VS 2017能够使用可为空的引用类型和静态本地方法(两者均为C#8功能)来编译小型测试库:

However, if you really want to you can now use C# 8 in Visual Studio 2017 by using the same trick that brings C# 7 to Visual Studio 2015: install the latest version of the Microsoft.Net.Compilers Nuget package into the project. It works, but of course VS 2017 doesn't know about C# 8 syntax so it doesn't look very pretty. Here's a screenshot showing that VS 2017 is able to compile a small test library using nullable reference types and a static local method (both of which are C# 8 features):

如果要尝试，请使用.csproj和代码:

Here's the .csproj and code if you want to try it:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFrameworks>netstandard2.0;net452</TargetFrameworks>
    <LangVersion>8.0</LangVersion>    
    <Nullable>enable</Nullable>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.Net.Compilers" Version="3.3.1">
      <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
    </PackageReference>
  </ItemGroup>
</Project>

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using System;

namespace CSharp8Test
{
    public class Class1
    {
        public string? NullableString { get; } = "Test";

        public static void Test()
        {
            Console.WriteLine(Test2());
            static int Test2() => 5;
        }
    }
}