Pop quiz, what does this do?

[Max Haughton]

On Wednesday, 3 March 2021 at 16:06:48 UTC, Steven Schveighoffer 
wrote:
> The FieldNameTuple from std.traits returns a tuple of names of 
> all the fields that are present on a type instance.
>
> What about the result on things that can't have fields?
>
> import std.traits;
>
> interface I
> {
>    int foo();
> }
>
> pragma(msg, FieldNameTuple!I);
>
> Without looking up the docs, or trying it, what do you think it 
> does?
>
> -Steve

"" - difference between a field and a member I'm guessing