C# Performance: Value Types vs Reference Types Guide

Picture this: you’re debugging a C# application that’s slower than molasses in January. Memory usage is off the charts, and every profiling tool you throw at it screams “GC pressure!” After hours of digging, you realize the culprit: your data structures are bloated, and the garbage collector is working overtime. The solution? A subtle but powerful shift in how you design your types—leveraging value types instead of reference types. This small change can have a massive impact on performance, but it’s not without its trade-offs. Let’s dive deep into the mechanics, benefits, and caveats of value types versus reference types in C#.

Understanding Value Types and Reference Types

In C#, every type you define falls into one of two categories: value types or reference types. The distinction is fundamental to how data is stored, accessed, and managed in memory.

Value Types

Value types are defined using the struct keyword. They are stored directly on the stack (in most cases) and are passed by value. This means that when you assign a value type to a new variable or pass it to a method, a copy of the data is created.

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

Point p1 = new Point { X = 10, Y = 20 };
Point p2 = p1; // Creates a copy of p1
p2.X = 30;

Console.WriteLine(p1.X); // Output: 10 (p1 is unaffected by changes to p2)

In this example, modifying p2 does not affect p1 because they are independent copies of the same data.
Reference Types
Reference types, on the other hand, are defined using the class keyword. They are stored on the heap, and variables of reference types hold a reference (or pointer) to the actual data. When you assign a reference type to a new variable or pass it to a method, only the reference is copied, not the data itself.
class Circle
{
    public Point Center;
    public double Radius;
}

Circle c1 = new Circle { Center = new Point { X = 10, Y = 20 }, Radius = 5.0 };
Circle c2 = c1; // Copies the reference, not the data
c2.Radius = 10.0;

Console.WriteLine(c1.Radius); // Output: 10.0 (c1 is affected by changes to c2)

Here, modifying c2 also affects c1 because both variables point to the same object in memory.

💡 Pro Tip: Use struct for small, immutable data structures like points, colors, or dimensions. For larger, mutable objects, stick to class.

Performance Implications: Stack vs Heap
To understand the performance differences between value types and reference types, you need to understand how memory is managed in C#. The stack and heap are two areas of memory with distinct characteristics:
    

        

            

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