C# Performance & Design: When to Use record vs class

 C# Performance & Design: When to Use record vs class

In modern C# development (C# 9 through C# 13), choosing between a class and a record (or record struct) is a fundamental architectural decision. While both represent data structures, they serve entirely different paradigms in software design: Object-Oriented Mutability versus Data-Centric Immutability.

1. Fundamental Differences

• Value Equality vs Reference Equality: Classes compare references by default (two separate objects with identical property values are NOT equal). Records automatically implement value-based equality.
• Immutability by Default: Record positional syntax automatically generates init-only properties, preventing accidental side effects in multi-threaded environments.
• Built-in Formatting: Records automatically override .ToString() to display formatted property names and values, whereas classes display the type's namespace string by default.
• Nondestructive Mutation: Records support the with expression, allowing you to create shallow copies with modified properties effortlessly.

 

2. Comparison Matrix

Feature	class	record (Reference Type)
Primary Use Case	Domain Entities, Business Logic, Services	DTOs, API Requests/Responses, Value Objects
Default Equality	Reference Equality	Value-Based Equality
Immutability	Mutable by default (get; set;)	Immutable by default (init)
Mutation Syntax	Direct assignment (obj.Prop = x)	with expressions (obj with { Prop = x })
ToString() Output	Namespace.ClassName	RecordName { Prop = Val }

 

3. Principal Engineer Rules of Thumb

1. Use Records for Data Containers: Data Transfer Objects (DTOs), API Contracts, Event Bus Messages, and Value Objects should be record types.
2. Use Classes for Stateful Entities & Services: Database models with lifecycle states (EF Core Entities), Dependency Injection services (Services, Repositories), and stateful domain objects belong in class structures.
3. Threading Safety: Favor record for concurrent systems—immutable data eliminates race conditions by default.