Interactive Window

Kasey Uhlenhuth. GitHub. dotnet/roslyn. 2015-11-24.
The C# Interactive Window provides a fast and iterative way to learn APIs, experiment with code snippets, and test methods by giving immediate feedback on what an expression will return or what an API call does.
The C# Interactive Window is a read-eval-print-loop (REPL) with advanced editor support. It supports features like IntelliSense as well as the ability to redefine functions & classes. After entering a code snippet–which can contain class and function definitions at top-level along with statements–the code executes directly. This means you no longer need to open a project, define a namespace, define a  Main  method, add a  Console.WriteLine()  call to output your result, and add a  Console.ReadLine()  call in order to play with code. In other words, say goodbye to ConsoleApp137 or whatever ridiculously high number your Console Apps default to today!

[Interactive Window]

Going Interactive with C#

Tom Fischer. Simple Talk.  
For some time now, C# programmers have gazed enviously at the interactive capabilities of F#, Python and PowerShell. For rapid prototyping work and interactive debugging, dynamic languages are hard to beat. C# Interactive slipped into view quietly, without razzmatazz, in Visual Studio 2015 Update 1. It’s good, it’s worth knowing about; and Tom Fischer is intent on convincing you of that.
It became easier to explore both C# code snippets and APIs with the release of Visual Studio 2015 C# Interactive, which arrived with Update 1. If you think that it is just a scripting utility then it is likely that you are missing out on a valuable way of becoming more productive as a developer.
It might be more accurate to classify it as C# REPL tool with scripting support. As such, it has obvious value as a great time-saver. Within a REPL environment, C# developers can rapidly do such things as code prototypes, explore unfamiliar data, learn APIs and write complex tests. Readers who are familiar with languages such as F#, PowerShell and Python, already enjoy such capabilities. It’s now available to the C# developer as well.
This article introduces C# Interactive and aims to show how it can boost any C# developer’s productivity.

[Going Interactive with C#]