Difference of is null vs equals null and why is null is recommended

Difference of is null vs equals null and why is null is recommended

Both C# is null and == null are used to check if a variable or object is null, but they work slightly differently.

  • is null checks if the variable or object is of a nullable type and has a value of null.
  • == null compares the variable or object to the literal value of null.

For example,

string? str = null;
if (str is null) {
    // this block will execute

if (str == null) {
    // this block will also execute

is null is a feature of C# 8.0 and above, so it will not work in older versions of C#.

One of the main benefits of using is null is that it is more readable and self-explanatory. When reading code, it is immediately clear that the developer is checking for a null value, without having to infer the meaning from the comparison operator. This can make the code easier to understand for both the original developer and anyone else who may need to read or maintain the code in the future.

See recommendation by Jared Parsons who is working on the C# compiler, language and runtime.

https://twitter.com/jaredpar/status/1229850618749050880 I was trying to be good but now that you've called me out ... You should always use "x is null" and "x is object" for null and non-null reference checks respectively. They're demonstrably better than all other alternatives.

Another advantage of is null is that it is more specific and less prone to errors. When using == null, the developer may accidentally compare a non-nullable variable to null, which will cause a runtime error.\ However, is null can only be used with nullable types, which eliminates this possibility and makes the code more reliable.
Additionally, is null can also be used as a pattern matching expression. This allows developers to simplify their code by combining null checking with variable assignment, as shown in the following example:

string? s = GetString();
if (s is null)
    Console.WriteLine("string is null");

Analyzer proposal: Discourage == null and != null syntax