When to Use Records, Classes, and Structs in .NET: A Comprehensive Guide

Choosing the right data type in .NET is crucial for effective data management and manipulation. If your data type can be a value type, use a struct. If it describes a value-like, preferably immutable state, use a record. Otherwise, use a class. Here's a quick guide:

1. Structs

Structures, or structs, are value types in .NET. They are ideal for representing small, simple objects that have a limited scope and are not intended to be modified. Structs are particularly useful when you want to ensure that each instance of a data type holds its own copy of the data, rather than a reference to shared data.

Characteristics

• Value Type: Holds data directly.

• Small Size: Typically used for data structures with an instance size under 16 bytes.

• Immutability: Often used for immutable data structures, although they can be mutable.

• Performance: Avoids the overhead of heap allocation and garbage collection, making them efficient for small, frequently used objects.

Use Cases

• Primitive-Like Values: Ideal for single-value logical representations similar to int, double, etc.
• Small Data Structures: Useful for small, lightweight data structures that do not require complex behaviors or relationships.

Example

public struct Point
{
    public int X { get; }
    public int Y { get; }

    public Point(int x, int y)
    {
        X = x;
        Y = y;
    }
}

2. Records

Records are a relatively new addition to .NET, introduced to provide an immutable, value-oriented reference type.

Characteristics'

• Reference Type: Similar to classes but designed with immutability in mind.

• Immutability: By default, records are immutable, but they can be made mutable if needed.

• Shallow Copy: Assigning a record creates a shallow copy; the with expression provides a specialized cloning mechanism.

Use Cases

• Data Transfer Objects (DTOs): Perfect for representing data that flows in one direction.
• Immutable Request Bindings: Ideal for scenarios where data should not change after creation.
• Search Parameters: Suitable for defining immutable search parameters.

Example

public record Person(string FirstName, string LastName);

Example of Shallow Copy

var original = new Foo("a");
var copy = original with { MutableProperty = 15 };

1. Classes

Classes are reference types in .NET, designed to support complex data structures and relationships. They are suitable for scenarios where you need objects to reference other objects, enabling hierarchical data structures and behaviors.

Characteristics

• Reference Type: Holds references to data, allowing multiple references to the same object.
• Complexity: Supports inheritance and polymorphism, making them suitable for complex hierarchies.
• Mutability: Can be either mutable or immutable, depending on the design

Use Cases

• Hierarchical Data Structures: Ideal for representing complex relationships and behaviors through inheritance.
• Complex Objects: Suitable for objects that require methods, events, and encapsulated logic.
• Shared References: Useful when multiple references to the same object are needed.

Example

public class Animal
{
    public string Name { get; set; }

    public void Speak()
    {
        Console.WriteLine("Animal speaks");
    }
}

Summary

Choosing the right data type in .NET depends on the characteristics and requirements of your data. Here's a quick guide to help you decide:

• Can your data type be a value type? If yes, go with a struct.
• Does your type describe a value-like, preferably immutable state? If yes, go with a record.
• Use a class otherwise.

In practical terms

1. Yes, use records for your DTOs if it is a one-way flow.
2. Yes, immutable request bindings are an ideal use case for a record.
3. Yes, SearchParameters are an ideal use case for a record.

This approach ensures you select the most appropriate data type based on your specific needs and the behavior you expect from your data structures.