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?

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. — Rob Powell, Dec 04 '18 at 12:56
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! — Heinzi, Dec 04 '18 at 12:57
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. — mjwills, Dec 04 '18 at 13:01
Can't repro with 15.9.3. Can't even access the property `c` in `MyList[0].c` with the debugger: _"'System.ValueTuple' does not contain a definition for 'c' and no extension method 'c' accepting a first argument of type 'System.ValueTuple' could be found (are you missing a using directive or an assembly reference?) "_ — Tim Schmelter, Dec 04 '18 at 13:02
@Heinzi 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. — Rob Powell, Dec 04 '18 at 13:09
@Rango I can repro it in 15.9.3. Make sure to use `MyList[0].b` or `MyList[0].c` as the Watch expression. — Peter B, Dec 04 '18 at 13:11
@PeterB: i can't use those properties as i've mentioned above. And if i use the exact code in this [bug report](https://github.com/dotnet/roslyn/issues/28151) it correctly shows `123` for `Item1` and `"abc"` for `Item2`. .NET version: 4.7.03056, Language Level: C# 7.2 — Tim Schmelter, Dec 04 '18 at 13:12

Heinzi · Accepted Answer · 2018-12-04T13:35:44.887

4

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.

edited Dec 04 '18 at 13:35

answered Dec 04 '18 at 13:04

Heinzi

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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. – Tim Schmelter Dec 04 '18 at 13:07
@Rango: Good point. If you feel like it, you might want to add that as a comment to the github issue. – Heinzi Dec 04 '18 at 13:18

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

1 Answers1