How to use C# 7 with Visual Studio 2015?

Question

Visual Studio 2017 (15.x) supports C# 7, but what about Visual Studio 2015 (14.x)?

How can I use C# 7 with it?

Answer 1

You can replace the compiler shipped with Visual Studio for a C# 7-enabled version by installing the Nuget package Microsoft.Net.Compilers:

Referencing this package will cause the project to be built using the specific version of the C# and Visual Basic compilers contained in the package, as opposed to any system installed version.

There is no indication that I can see on the package page as to whether this is officially supported in Visual Studio 2015. My not-thorough tests so far indicate that it works but not painlessly - C# 7 code compiles, but is underlined with the red squiggly line which indicates a syntax error: Note that you will also need to install the Nuget package System.ValueTuple to use the new C# 7 value tuples features.

Answer 2

In my case, installing just Microsoft.Net.Compilers didn't work. Instead, I had to do the following:

1. Install Microsoft.CodeDom.Providers.DotNetCompilerPlatform for the project (Tools => NuGet Package Manager => Manage Nuget Packages for Solution...) and install Microsoft.CodeDom.Providers.DotNetCompilerPlatform.
2. Install the latest Microsoft.Net.Compilers for the project
3. Install any other NuGet package for the latest C# feature you want to use. In my case, my goal was to use Tuples, so I installed System.ValueTuple and worked fine.

But still note that C# codes which are not known by Visual Studio 2015 default compiler will still have red squiggles underneath.