C# Feature - with expressions

Overview

With expressions provide non-destructive mutation by copying an existing record or struct and applying targeted changes.

Introduced In

C# 9.0 (2020)

Before

var updated = new Person(existing.Name, 37);

After

var updated = existing with { Age = 37 };

Gotchas & Best Practices

• With expressions shine most with immutable data models.
• Use them with records or value objects that should not be mutated in place.