Interaction of `var`, `nameof`, and `Color Color`

[KalleOlaviNiemitalo]

C# 7 draft §13.6.2 (Local variable declarations) says this about "implicitly typed local variable declaration":

The initializer expression cannot refer to the declared variable itself

As specified and implemented, this disallows also var x = nameof(x); even though the type of the expression would be unambiguous in this case. That was discussed in dotnet/roslyn#766 and C# Design Meeting Notes for Mar 4, 2015.

However, the wording "refer to the declared variable" seems a bit ambiguous in the "Color Color" case (C# 7 §12.8.7.2, Identical simple names and type names).

In the following example, does nameof(Color.Beige) refer to the variable, the type, or both?

class C {
    void M() {
        var Color = nameof(Color.Beige) == "nope" ? (Color)1 : (Color)2;
    }

    enum Color {
        Beige,
        Mauve,
        Fuchsia,
    }
}

(Continued from #831 (comment))

[KalleOlaviNiemitalo]

A similar example without nameof:

class C {
    void M() {
        var Color = Color.Beige;
    }

    enum Color {
        Beige,
        Mauve,
        Fuchsia,
    }
}

Here, to find the type of the initialiser expression Color.Beige, the compiler needs to check whether the Color Color rule applies, and for that, it needs to know the type of the Color variable, which in turn depends on the type of the expression. So the standard should forbid this. I'm not sure whether it currently does.

[jskeet]

Thanks for this - we're currently focusing on getting C# 7 "done" and probably won't get to this for a while, but we'll look carefully when we get a chance.

[jskeet]

Given that this doesn't look like it's directly related to a C# 7 feature (so was already broken in C# 7) I'm going to punt this to C# 8. As ever, feel free to disagree if I've missed something.

[jskeet]

We've discussed this again, and find it a fascinating topic - but probably not our highest priority right now, unfortunately.

Not moving this from the C# 8 milestone as we'd still like to try to get it done for C# 8 - but we won't let it block the release if we're facing a deadline.