Unable to return Tuple from a method using Visual Studio 2017 and C# 7.0

Question

I\'ve installed Visual Studio 2017 Community that was released a week ago, and I started exploring the new features of C# 7.

So I created a simple method that return

Answer 1

I got this error too after updating to .NET 4.7.2 and was able to fix it by re-installing nuget packages using:

Update-Package -Reinstall

Answer 2

I started getting this error after I installed .Net 4.7 Framework, and changed my project to target .Net 4.7

ValueTuple is now included with .Net 4.7, so you don't have to reference the ValueTuple manually.

All I had to do to correct the compile error was remove the reference to System.ValueTuple from my project's references.

Answer 3

I Just ran through this page on Roslyn which describes the following steps to get this working:

1. Start a C# project
2. Add a reference to the System.ValueTuple package from NuGet (pre-release)

Following those steps, it is now working. But it is really very weird that we need to do that for every single project that we start! Hope this is fixed when we reach the Official release!

Answer 4

I also came accross this issue as I upgraded from .NET 4.6.2 to .NET 4.7.2. Unfortunately, I was not able to remove the package reference to System.ValueTuple because another NuGet package I use depends on it.

Finally I was able to locate the root cause: There was a .NET 4.6.2 version of mscorlib.dll lying around in the project folder (output of a publish operation) and MSBuild decided to reference this assembly instead of the official .NET 4.7.2 reference assembly located in C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2.

Due to the fact that System.ValueTuple was introduced in .NET 4.7, MSBuild failed the compilation because it could not find the type in the reference assembly of .NET 4.6.2.