EDIT [Nov 29 2020]: .NET 5.0 is out now, but the solution below is still required if you're targetting .NET Standard 2.1
C# 9.0 is still under development. There are a couple references which lead me to believe it should be testable now (some of it, anyway).
- A Microsoft blog by Mr. Awesome himself, introducing the features. https://devblogs.microsoft.com/dotnet/welcome-to-c-9-0/
- The language tracking page on github: https://github.com/dotnet/roslyn/blob/master/docs/Language%20Feature%20Status.md
I'm using VS 2019 16.7 Preview 3.1. I've selected the language version as Preview for a project.
Some C# 9 features, I can use. Like: Dictionary<string, object> Stuff = new()
But using the new init
feature gives me this error: Error CS0518 Predefined type 'System.Runtime.CompilerServices.IsExternalInit' is not defined or imported
How do I fix this?
Examples of code causing the error:
class Test
{
public int Hello { get; init; }
}
and
record Test(int hello);
The record definition is shorthand and expands into something that uses init
, which is why it's also affected.
The language tracking page I linked to above says the feature was Merged into 16.7p3
, which I am using.
Am I just being overly excited? Do I need to wait? Or is there a way to play with these features right now :D
EDIT (requested in comments) - Adding csproj for .net 5.0 console app:
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net5.0</TargetFramework>
<LangVersion>preview</LangVersion>
</PropertyGroup>
</Project>
EDIT #2: A workaround posted here - https://github.com/dotnet/roslyn/issues/45510
See Question&Answers more detail:
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