Champion "tuple projection initializers" (C# 7.1, VB 15.3)

[jcouv]

• Proposal added infer-tuple-names.md
• Discussed in LDM (2017-04-05)
• Decision in LDM (and reviewed with compat council)
• Finalized (done, rejected, inactive)
• Spec'ed

See also #370
A working implementation is at dotnet/roslyn#18374

[NickCraver]

Can you please fix the link in https://github.com/dotnet/roslyn/blob/master/docs/Language%20Feature%20Status.md when the proposal is added?

[jcouv]

@NickCraver Will do. I think the link will actually be correct, but I need to write the document.

[DavidArno]

@jcouv,

I have run into an issue with this feature in Preview 7.0 of VS2017 Update 3. Consider the following example code:

public static void Foo()
{
    (T1, T2) Bar<T1, T2>((T1, T2) value) => value;

    var tuple = (a:1, b:2);
    var newTuple = Bar(tuple);
    var a = newTuple.a;
}

I get an error, "(int, int)' does not contain a definition for 'a' and no extension method 'a' accepting a first argument of type '(int, int)' could be found..." on the last line.

When it comes to generics, this tuple name inference appears to be limited to having to express the whole tuple as, eg T. If I change the code to:

public static void Foo()
{
    T Bar<T>(T value) => value;

    var tuple = (a:1, b:2);
    var newTuple = Bar(tuple);
    var a = newTuple.a;
}

then the code compiles. But then, my Bar isn't restricted to a two item tuple; it'll take any type. As ValueTuple<T1, T2> is a struct, I can't constrain T using generic constraints either.

Is this a bug/oversight, or is what I want to do completely outside the scope of this new feature?