Predefined type System ValueTuple 2 is not defined or imported

Question

I ve installed Visual Studio 15 Preview 3 and tried to use the new tuple feature  static void Main string   args        var x   DoSomething        Console WriteLine x x      static  int x  int y  DoSomething         return  1  2       When I compile I get the error      Predefined type  System ValueTuple  2   is not defined or imported   According to the blog post  this features should be  on  by default    What did I do wrong

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In case others have the same problem  I ran into this error after updating a project to 4 7  Oddly enough  I had to remove the System ValueTuple reference for this error to go away

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It s part of the  NET Framework 4 7   As long as you don t target the above framework or higher  or  NET Core 2 0    NET Standard 2 0   you ll need to reference ValueTuple  Do this by adding the System ValueTuple NuGet Package

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I would not advise adding ValueTuple as a package reference to the  net Framework projects  As you know this assembly is available from 4 7  NET Framework   There can be certain situations when your project will try to include at all costs ValueTuple from  NET Framework folder instead of package folder and it can cause some assembly not found errors   We had this problem today in company  We had solution with 2 projects  I oversimplify that      Lib Web   Lib was including ValueTuple and Web was using Lib  It turned out that by some unknown reason Web when trying to resolve path to ValueTuple was having HintPath into  NET Framework directory and was taking incorrect version  Our application was crashing because of that  ValueTuple was not defined in  csproj of Web nor HintPath for that assembly  The problem was very weird  Normally it would copy the assembly from package folder  This time was not normal   For me it is always risk to add System   package references  They are often like time-bomb  They are fine at start and they can explode in your face in the worst moment  My rule of thumb  Do not use System   Nuget package for  NET Framework if there is no real need for them   We resolved our problem by adding manually ValueTuple into  csproj file inside Web project

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Make sure you have  NET 4 6 2 Developer Pack for VS installed and then pull in System ValueTuple package from NuGet

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For  NET 4 6 2 or lower   NET Core 1 x  and  NET Standard 1 x you need to install the NuGet package System ValueTuple   Install-Package  System ValueTuple    Or using a package reference in VS 2017    lt PackageReference Include  System ValueTuple  Version  4 4 0    gt     NET Framework 4 7   NET Core 2 0  and  NET Standard 2 0 include these types

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The ValueTuple types are built into newer frameworks     NET Framework 4 7   NET Core 2 0  Mono 5 0   Net Standard 2 0   Until you target one of those newer framework versions  you need to reference the ValueTuple package   More details at http   blog monstuff com archives 2017 03 valuetuple-availability html

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I had to check System ValueTuple dll file was under source control and correct its reference in  cssproj files    rightclick each project in solution unload project edit  cssproj file  change    lt  Reference Include  System ValueTuple      lt  HintPath         ProjectName ProjectName obj Release Package PackageTmp bin System ValueTuple dll    lt   HintPath     lt   Reference    into    lt  Reference Include  System ValueTuple      lt  HintPath        packages System ValueTuple 4 4 0 lib netstandard1 0 System ValueTuple dll    lt   HintPath     lt   Reference     save changes and reload projects find System ValueTuple dll and save it into this folder add reference of this file into source control    Optional   7  solve same problems with another  dll files this way

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For Visual Studio Code use the built in Terminal and run   dotnet add package  System ValueTuple    Don t forget to run dotnet restore afterwards

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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    duplicate of https   stackoverflow com a 57777123 128709

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We were seeing this same issue in one of our old projects that was targeting Framework 4 5 2  I tried several scenarios including all of the ones listed above  target 4 6 1  add System ValueTuple package  delete bin  obj  and  vs folders  No dice  Repeat the same process for 4 7 2  Then tried removing the System ValueTuple package since I was targeting 4 7 2 as one commenter suggested  Still nothing  Checked csproj file reference path  Looks right  Even dropped back down to 4 5 2 and installing the package again  All this with several VS restarts and deleting the same folders several times  Literally nothing worked   I had to refactor to use a struct instead  I hope others don t continue to run into this issue in the future but thought this might be helpful if you end up as stumped up as we were

[c#] Predefined type 'System.ValueTuple´2´ is not defined or imported

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