Overload resolution for FormattableString (bug?)

[rikimaru0345]

Hello, I have three small questions.

1. Calling L($"some {i} formatted string"); will use the string overload
   instead of the FormattableString given those two methods:

public static string L(FormattableString fs)
	=> string.Format(fs.Format, fs.GetArguments());

public static string L(string s)
	=> s;

2. When you just have the following (now an extension method), you cannot call it
   like this $"test {i} string".L();

public static string L(this FormattableString fs)
{
	return string.Format(fs.Format, fs.GetArguments());
}

Is the second one really supposed to not work, calling L(...) directly will work though.
As for the first one, since FormattableStringis more rarely used, shouldn't it have higher priority?
It would make things a little easier.

3. Why isn't FormattableString not a struct? It always allocates, couldn't that have been prevented easily?

I hope someone can explain if this is just an unintended side-effect, or if there's any actual reasoning behind this behaviour.

[yaakov-h]

dotnet/roslyn#173
dotnet/roslyn#518
dotnet/roslyn#8097

[rikimaru0345]

I read the threads you linked.
Wow... that sucks.

99% of the users could live without being able to sub-class FormattableString (they can write a library or something), but bad performance can't be fixed. Really sad. Bad decisions.