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.