Structs vs. Classes in C# and .NET Core

In C#, both

code

struct

and

code

class

are used to define custom data types. However, they have fundamental differences in how they are stored in memory, how they are passed around, and their behavior, which significantly impacts performance and design decisions, especially when working with .NET Core and integrating with services like Azure.

Core Differences: Value vs. Reference Types

The most crucial distinction lies in their memory management.

code

struct

types are value types, meaning the variable directly contains the data.

code

class

types are reference types, where the variable holds a reference (a memory address) to the actual object data, which is stored on the heap.

Structs are value types, classes are reference types.

Value types (structs) are stored directly where the variable is declared (stack or inline within another object). Reference types (classes) store a reference to the object's location on the heap.

When you assign a struct variable to another, the entire value is copied. When you assign a class variable to another, only the reference is copied, meaning both variables point to the same object in memory. This has significant implications for mutability and performance.

Memory Allocation: Stack vs. Heap

Structs are typically allocated on the stack, which is managed automatically and is very fast for allocation and deallocation. Classes are allocated on the managed heap, which involves garbage collection, a more complex process that can introduce overhead.

Where are structs typically allocated in memory?

On the stack.

Where are class objects typically allocated in memory?

On the heap.

Passing Arguments: Copy vs. Reference

When you pass a struct to a method, a copy of the struct is made. When you pass a class instance to a method, a copy of the reference is made. This means modifications to a struct within a method do not affect the original struct, while modifications to a class instance within a method do affect the original instance.

Passing structs by value can lead to performance issues if the struct is large, due to the cost of copying. Consider using ref or in keywords for large structs if you need to avoid copying.

Inheritance and Polymorphism

Classes support inheritance, allowing them to derive from other classes and implement interfaces. Structs, on the other hand, cannot inherit from other structs or classes (though they can implement interfaces). This makes classes more flexible for building complex object hierarchies.

Feature	Struct	Class
Type	Value Type	Reference Type
Memory Allocation	Stack (typically)	Heap
Assignment Behavior	Copies value	Copies reference
Inheritance	Cannot inherit from classes/structs	Supports inheritance
Default Value	All members initialized to default	Null
Nullability	Cannot be null (unless Nullable<T>)	Can be null

When to Use Structs vs. Classes

Use structs for small, immutable data types that logically represent a single value, similar to primitive types (like

code

int

code

double

). Examples include points, colors, or simple coordinate systems. They are ideal when you want to avoid the overhead of heap allocation and garbage collection.

Use classes for larger, mutable data types, or when you need to leverage inheritance, polymorphism, or object identity. Most complex application objects, services, and entities are best represented as classes.

Visualizing the memory difference: Imagine a struct as a physical box containing its contents, and a class as a label pointing to a storage unit elsewhere. Copying a struct is like making a duplicate box. Copying a class is like making a duplicate label pointing to the same storage unit. This difference is crucial for understanding how changes propagate.

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Implications for Azure Integration

When designing data models for Azure services (e.g., Azure Cosmos DB, Azure Storage Queues, Azure Service Bus), understanding structs vs. classes is vital for performance and serialization. Small, value-like data structures might be more efficiently handled as structs, especially in high-throughput scenarios, as they can reduce memory pressure and garbage collection cycles. However, complex entities with relationships and behaviors are naturally modeled as classes.

What is a key consideration when choosing between structs and classes for Azure data models?

Performance and serialization efficiency, especially in high-throughput scenarios.

Learning Resources

Structs (C# Programming Guide)(documentation)

The official Microsoft documentation detailing the definition, usage, and characteristics of structs in C#.

Classes (C# Programming Guide)(documentation)

Comprehensive documentation from Microsoft on C# classes, covering their features, instantiation, and behavior.

Value Types and Reference Types(documentation)

An in-depth explanation of the fundamental difference between value types (structs) and reference types (classes) in C#.

C# Structs vs Classes: When to Use Which(blog)

A practical guide that breaks down the differences and provides clear scenarios for choosing between structs and classes.

Understanding Value Types and Reference Types in C#(video)

A visual explanation of value types and reference types, including how they are handled in memory and passed to methods.

C# Performance: Structs vs Classes(blog)

An article that delves into the performance implications of using structs versus classes, with practical examples.

Structs and Classes in C# - A Deep Dive(tutorial)

A detailed tutorial covering the syntax, behavior, and key differences between structs and classes in C#.

C# Memory Management: Stack vs Heap(video)

This video provides a clear explanation of how the stack and heap memory work in C#, which is fundamental to understanding structs vs. classes.

Structs in C# - GeeksforGeeks(blog)

GeeksforGeeks offers a concise overview of C# structs, highlighting their key features and differences from classes.

C# Performance Tips: Structs(documentation)

A section from a well-regarded C# reference book discussing performance considerations, including the use of structs.