Why does the Visual Studio watch window show wrong values for ValueTuples in a collection?

Question

I'm finding that ValueTuples evaluate differently when I access their properties from a collection.

    public static List<Tuple<string, bool>> MyTupleList = new List<Tuple<string, bool>>
    {
        new Tuple<string, bool>("test", true)
    };

    public static List<(string b, bool c)> MyList = new List<(string b, bool c)>
    {
        ("test", true)
    };

Why do these two highlighted lines evaluate differently and how can I change "MyList[0].c" to get the value correctly?

Liverwurst

How is MyTupleList related which is not a ValueTuple? – Sempach

I simply included it to highlight the evaluation of the Tuple type "MyTupleList[0].Item1" working when "MyList[0].Item1" doesn't. Probably should have mentioned that in my question. – Liverwurst

Can you reproduce this in code (accessing MyList[0].c yields the wrong value) or is this just a problem with the Visual Studio tool window? If the latter: This is a Visual Studio issue (and not a C# issue), so please include the precise VS version in your question and tag it with visual-studio-{version}. If the former: Please provide a full repro example. Oh, and good question, by the way! – Inhabited

This seems to be an issue with the Immediate Window and other tooling (Watch Window etc) - it doesn't affect the app itself. I can repro it in VS 15.8.4, .NET Core 2.1. – Pruitt

Can't repro with 15.9.3. Can't even access the property c in MyList[0].c with the debugger: "'System.ValueTuple<string,bool>' does not contain a definition for 'c' and no extension method 'c' accepting a first argument of type 'System.ValueTuple<string,bool>' could be found (are you missing a using directive or an assembly reference?) " – Sempach

@Inhabited it seems to evaluate correctly if I write the line in code. So it looks like it may just be the Visual Studio tool windows. I found the issue using the C# immediate window and then replicated in the watch window. My Visual Studio version is 15.8.9. I'll add the tag. – Liverwurst

@Rango I can repro it in 15.9.3. Make sure to use MyList[0].b or MyList[0].c as the Watch expression. – Celebes

@PeterB: i can't use those properties as i've mentioned above. And if i use the exact code in this bug report it correctly shows 123 for Item1 and "abc" for Item2. .NET version: 4.7.03056, Language Level: C# 7.2 – Sempach

Answer 1

This seems to be a bug in Visual Studio 2017.

There are a few related bugs mentioned on Roslyn's github issue tracker, e.g.:

• Watch window doesn't handle List<Tuple> properly - which is still open but seems to be fixed (when accessing the value as Item1), see Rango's comment.
• Debugger can't evaluate list[0].first if T=ValueTuple - moved to the internal Visual Studio bug tracker, since this is not related to the compiler.

Since the issue tracker of Visual Studio is not public, we can only wait and hope that these bugs get fixed.

Inhabited

It seems to be fixed in VS 2017 v15.9.3. Because i can't access c in the debugger and if i use Item1 or Item2 i get the correct values(so not null or false). Maybe it's still open because you can't access the named properties in the debugger. – Sempach

@Rango: Good point. If you feel like it, you might want to add that as a comment to the github issue. – Inhabited