An update to C# versions and C# tooling

Phillip Carter

Phillip

Starting with Visual Studio 2019 Preview 4 and RC, we’ll be adjusting how C# versions are treated in .NET tooling. The version of C# used by your project will now be determined by target framework.

Summary of changes

The most important change is that the version of C# used by tooling by default will be determined by the target framework of your project.

Additionally, we are adding two new Language Version (LangVer) values: LatestMajor and Preview. Here’s how they stack up compared with the currently supported list of values:

LangVersionMeaning
ISO-1C# 1.0/1.2
ISO-2C# 2.0
3C# 3.0
4C# 4.0
5C# 5.0
6C# 6.0
7C# 7.0
7.1C# 7.1
7.2C# 7.2
7.3C# 7.3
8.0C# 8.0
LatestMajorLatest supported major C# language version
PreviewLatest available preview C# language version
LatestLatest supported C# language version (including minor version)

 

The meaning of “supported C# language version” differs based on target, and the default used is also determined by the target of your project.

How this works for .NET Core 3.0 and .NET Standard 2.1

C# 8.0 has been built with .NET Core 3.0 and .NET Standard 2.1 in mind. Many of its features only work on .NET Core 3.0. This means .NET Core 3.0 and .NET Standard 2.1 are the only .NET Core and .NET Standard versions where C# 8.0 is supported.

How this works for all other target frameworks

Because C# 8.0 has been built for .NET Core 3.0 and .NET Standard 2.1, it will not be supported outside of .NET Core 3.0 and any platform implementing .NET Standard 2.1.

Support and compatibility for preview features

This change means that C# 8.0 preview will be the default for .NET Core 3.0 preview in all .NET tools, including Visual Studio. The way to think about support in this world is slightly different than before. We distinguish support today along the following lines:

  • Any C# 7.3 and lower feature or behavior is fully supported and fully compatible in any context (.NET Core 3.0, .NET Core 2.x, .NET Framework, etc.). No change from what exists today.
  • Any C# preview feature is unsupported.
  • There is no compatibility guarantee from one C# preview to another.

In short, if you use C# 8.0 preview with Visual Studio 2019, some features and behaviors may change between now and when C# 8.0 fully releases.

Happy hacking!

Phillip Carter
Phillip Carter

Program Manager, .NET and Languages

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13 Comments
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Ilya Veselov 2019-02-27 13:41:39
What about the current LatestMinor value used in projects targeting the latest C# version, and how it will be migrated?
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MgSam 2019-02-27 14:41:53
So you're saying that C# 8.0 is not shipping with VS 2019? That is disappointing (but not entirely surprising given how many features are still in it). So will it be an out-of-band release or is it getting pushed back to VS 2020 or whatever the next VS version is?
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Tony Henrique 2019-02-27 16:53:23
This is the right move. New C# 8 features still need improvements and changes.
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Heinrich Moser 2019-02-28 02:31:10
Just out of curiosity: What was the rationale behind the previous "LatestMajor" default value? That option always struck me as odd: I don't want small (= low-risk) updates, but I do want large (= high-risk) updates? How does that make sense? (This is an honest question, not a rant!)
Stuart Lang
Stuart Lang 2019-02-28 03:01:41
I had to double take when I saw a C# post from you Phillip 😆 Have you got a promotion?
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SuperCocoLoco . 2019-03-01 04:50:08
I want to see the same evolution to Visual Basic.NET.
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Max Mustermann 2019-03-02 06:27:40
Where do I get netstandard2.1 preview? Using VS2019 Preview4/RC with latest netcore3.0 preview just gives me: error NETSDK1045: The current .NET SDK does not support targeting .NET Standard 2.1
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Koen Janssens 2019-03-25 00:12:43
Will this also apply fot VB.net?