Why is 'Predefined type 'System.ValueTuple' Unavailable' in Visual Studio 15 and how can I fix it?

Predefined Type 'System.ValueTuple' Unavailable

In Visual Studio 15 Preview 3, users face a compilation error when utilizing the new tuple feature. The error message reads, "Predefined type 'System.ValueTuple´2´ is not defined or imported."

Cause and Solution:

This issue arises when using .NET 4.6.2 or lower, .NET Core 1.x, or .NET Standard 1.x. To resolve this, install the NuGet package System.ValueTuple using the following command in PowerShell:

Install-Package "System.ValueTuple"

For Visual Studio 2017, use a package reference:

<PackageReference Include="System.ValueTuple" Version="4.4.0" />

For .NET Framework 4.7, .NET Core 2.0, and .NET Standard 2.0, these types are included by default.

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