'record' keyword not working in Visual Studio

Question

When I try to use the record keyword in my C# WPF .NET Framework file, it is recognised as a keyword, in the sense in appears in the code completion drop-down menu when you start typing, but then does not turn blue or work as it should.

keyword appearing in drop-down menu

When I use the record keyword, the error message is CS0246: The type or namespace name could not be found (are you missing a using directive or an assembly reference?).

error message when I use the keyword

According to what I've looked up, the record keyword should not need any special directives to use. I have also tried changing the .NET version, adding all the extra modifications in the visual installer, and repairing the installation many times.

I tested whether the keyword functioned correctly in some console apps. It worked in the regular .NET console app, but did not work in the .NET Framework console app.

Does anybody know a fix for this issue, or have any other ideas as to how I could tackle it? Thank you very much

Answer 1

The record keyword was introduced in C# 9.0: https://devblogs.microsoft.com/dotnet/welcome-to-c-9-0/#records

Its availability is dictated by your C# version, not your .NET version. This is often confusing but here's a doc from microsoft that helps clarify: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/language-versioning

Depending on what version of .NET Framework you're using you may or may not be able to use C# 9 or above, but you can try by adding <LangVersion>9.0</LangVersion> to your .csproj file and see if it compiles.

Answer 2

The record keyword was added in C# 9.

.NET Framework projects default to an older C# 7.3

The .NET (NOT framework) Console apps you see default to a higher version (10 for .NET 6, 11 for .NET 7, 12 for .NET 8), so that's why there are no issues there.

For .NET Framework, you could use records in a limited and possibly confusing and misleading way if you manually edited your csproj file and added <LangVersion>9.0</LangVersion> under <PropertyGroup>:

record Foo() // cannot inline declaration such as Foo(int Bar) due to no init support
{
    // no init modifier possible for the property
    public int NotInitOnlyProperty{ get; set; }
}

We don't get the init-only properties that are default for records, but we do get value equality and the with keyword.

var foo = new Foo();

// with works
var bar = foo with { NotInitOnlyProperty = 4 };

var baz = new Foo
{
    NotInitOnlyProperty = 4
};
Console.WriteLine(bar == baz); // true - value semantics

I haven't tested this more than the snippet above, so obvious disclaimers apply.