Unable to use the new extension members

[hez2010]

Version

0.8.0

What happened?

extension(string)
{
    public static string Hello => "Hello!";
}

Result:

(1,1): error CS9283: Extensions must be declared in a top-level, non-generic, static class.

[waf]

In order for this to work, it would require changes to Roslyn; it's a limitation of how roslyn scripting works, unfortunately.

In Roslyn Scripting, every type you declare in a submission becomes a nested type. This is generally incompatible with extension methods, that must be non-nested, top-level, static classes. There is some basic support for older-style extension methods, in that you can just declare them loose:

public static string Hello(this string _) => "Hello!";

"".Hello()

But I don't know of any support, current or planned, for Roslyn to support newer extension members.

It could be possible to detect the extension member syntax and compile it to its own assembly, then reference that in CSharpRepl.

It could also be interesting for someone to contribute support to https://github.com/dotnet/roslyn -- that would be the best approach, but I'm not sure how involved that is.

[hez2010]

I think maybe it's better to open an issue in roslyn.

[waf]

I'm investigating opening a PR in roslyn for this. I found this PR dotnet/roslyn#3472 from many years ago that added normal extension methods to scripting (I see you found that too!). If it's a similar level of effort for extension blocks / members then I'll get a PR ready.

[waf]

I've opened PR dotnet/roslyn#84177 that fixes this.