Struct vs. Record vs. Class in C#

When working with C#, developers often encounter three primary data structures: structs, records, and classes. Each of these data types has its own distinct characteristics, use cases, and advantages. Understanding the differences between them is crucial for making informed decisions when designing your C# applications. In this article, we will delve into the nuances of structs, records, and classes, providing you with a detailed comparison to help you choose the right one for your specific scenario.

What are Structs, Records, and Classes?

Before diving into the comparison, let’s define each of these data structures:

Structs

A struct, short for “structure,” is a value type in C#. It is typically used for small, lightweight objects that do not require reference semantics. Structs are stored on the stack rather than the heap, which makes them more memory-efficient and faster to create and destroy.

Here’s a basic example of a struct in C#:

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

Records

Records were introduced in C# 9.0 as a more concise and immutable alternative to classes. They are suitable for representing data transfer objects (DTOs), plain old data (POD) objects, and other scenarios where immutability and value semantics are desired. Records automatically generate equality, hash code, and deconstruction methods, simplifying common operations.

Here’s an example of a record in C#:

public record Person
{
    public string FirstName { get; init; }
    public string LastName { get; init; }
}

Classes

Classes are reference types in C# and are used for creating objects with more complex behavior and state. They allow for inheritance and are generally used to model entities, services, or components within an application. Classes are stored on the heap, which gives them more flexibility but also incurs a slight performance overhead compared to structs.

Here’s an example of a class in C#:

public class Car
{
    public string Make { get; set; }
    public string Model { get; set; }
    public int Year { get; set; }
}

Comparison of Structs, Records, and Classes

Now that we have a basic understanding of each data structure, let’s compare them in various aspects:

1. Mutability

• Structs: By default, structs are mutable. You can change the values of their fields after creation. However, it is generally considered a best practice to make structs immutable to avoid unexpected side effects.
• Records: Records are immutable by default. The properties of a record cannot be changed once they are set, which helps ensure data integrity.
• Classes: Classes are mutable by default. You can modify the properties and fields of a class instance at any time unless they are explicitly marked as read-only.

2. Memory Allocation

• Structs: Structs are value types, and they are typically allocated on the stack. This means they are more memory-efficient and have a shorter lifespan compared to classes.
• Records: Records are also value types, and they are allocated on the stack like structs. This provides similar memory efficiency benefits.
• Classes: Classes are reference types, and their instances are allocated on the heap. This can lead to higher memory overhead and slower allocation and deallocation compared to structs and records.

3. Equality and Value Semantics

• Structs: Structs have value semantics. Two struct instances are considered equal if their fields have the same values.
• Records: Records are designed with value semantics in mind. They automatically generate equality and hash code implementations based on their properties.
• Classes: Classes have reference semantics. Two class instances are considered equal only if they reference the same object in memory, which may not be the same as having the same property values.

4. Default Constructors

• Structs: Structs do not have default constructors. You must initialize all fields when creating a struct instance.
• Records: Records automatically generate a default constructor that initializes all properties. This simplifies object creation.
• Classes: Classes can have default constructors if not explicitly defined. You can create instances of classes without specifying all property values.

5. Inheritance

• Structs: Structs cannot be used as base types for inheritance. They do not support inheritance.
• Records: Records cannot be used as base types either. They are primarily intended for representing data, not for inheritance hierarchies.
• Classes: Classes are the primary choice for implementing inheritance hierarchies in C#. They support base and derived classes.

6. Performance Considerations

• Structs: Structs are generally more performant for small, lightweight data structures due to their stack allocation and value semantics. However, copying large structs can be inefficient.
• Records: Records offer good performance for data structures where immutability and value semantics are desired. They are efficient for most use cases but may not be suitable for extremely performance-sensitive scenarios.
• Classes: Classes are less memory-efficient than structs and records due to heap allocation and reference semantics. They may incur a small performance overhead in comparison.

When to Use Structs, Records, or Classes?

The choice between structs, records, and classes depends on your specific requirements and the nature of the data or objects you are modeling:

• Use structs when:
• You need a small, lightweight data structure.
• You want value semantics.
• You are concerned about memory efficiency and performance.
• Use records when:
• You want immutability and value semantics.
• You are modeling data transfer objects (DTOs) or plain data structures.
• You want simplified equality and hash code implementations.
• Use classes when:
• You need a more complex object with behavior and state.
• You are working with inheritance hierarchies.
• You need reference semantics or support for nullable reference types.

Conclusion

In C#, structs, records, and classes serve distinct purposes and come with their own advantages and limitations. Choosing the right data structure depends on your specific needs, whether it’s optimizing for performance, ensuring immutability, or modeling complex behavior. Understanding the differences outlined in this article will help you make informed decisions when designing your C# applications, ultimately leading to more efficient and maintainable code.