Pattern Matching | Over as with null check

Microsoft Docs / The is type pattern expression

Recommendation

Use pattern matching with the is expression over the as operator with a null check.

Use:

if (sender is Button b)

Not:

Button b = sender as Button;

if (b != null)

Justification

Both the Roslyn and .NET Core runtime teams agree that using this language feature is desirable.

Arguments

✔ Tends to eliminate a line dedicated to using the as operator with a variable assignment.

✔ Potential 5-10% speed improvement.

❌ Require an understanding variable scoping rules for if statements and how the is expression works.

❌ Only available in C# 7.0+.

Performance

Benchmark code

Benchmark IL

Exceptions

Analyzers

Discussion

GitHub Discussion