TL;DR

if (myVar is not null) DoSomething();

New C# 9 keyword: not

One of the smaller (less headline grabbing) additions to C# 9 is pattern matching (enhancements). And one of the smaller, but probably one of the features that will be most used, is the ‘not’ keyword.

Previously a common ‘not null’ check would be:

// no longer recommended as equals operator can be over-ridden
if (myVar != null) DoSomething(); 

// hard to read
if (!(myVar is null)) DoSomething();

C# 9 version:

if (myVar is not null) DoSomething();

The not keyword is part of the enhanced pattern matching.

Refs:

• https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-9#pattern-matching-enhancements
• https://www.infoq.com/news/2020/07/CSharp-And-Or-Not/