When should I use a struct rather than a class in C#?

Below is a concise explanation of when to use a struct instead of a class in C#. Structs are value types, while classes are reference types. Although they often look similar, each type has important implications for memory usage, performance, and how data is copied or passed around in your program.

When to Use a Struct

1. Small, Immutable Data

   • Structs work best for small objects where all members are generally set at creation and do not change afterward.
   • This immutability avoids confusion about passing by value (copy semantics) vs. reference.

2. Value Semantics

   • If your data’s natural behavior is that “a copy is a completely independent version,” a struct might be more intuitive.
   • Examples: Point, Color, DateTime.

3. Performance for Simple Types

   • Placing a small amount of data on the stack can be slightly more performant than allocating and de-allocating on the managed heap (especially for short-lived objects).
   • However, large structs or frequent copying might negate any performance benefit.

4. No Inheritance

   • Structs do not support inheritance (other than implicitly from System.ValueType), so they’re well-suited for simple data models without complex hierarchies.

When to Prefer a Class

1. Mutable Data

   • If values frequently change, and you need reference behavior, a class is often more appropriate.
   • Classes are allocated on the heap and passed around by reference, avoiding copies on assignment.

2. Inheritance and Polymorphism

   • If you need custom inheritance hierarchies, interfaces plus dynamic behavior, or more complex object relationships, use a class.

3. Large or Complex Objects

   • Structs are copied entirely on assignment. If your struct grows large or you pass it around frequently, copying can become expensive.
   • Classes only pass references, which usually scales better for more complex scenarios.

Practical Guidelines

• Keep structs small—preferably 16 bytes or less—and consider immutability.
• Default to using classes unless you have a strong rationale for struct-like behavior.

Take Your C# Skills Further

Digging deeper into language fundamentals like value types vs. reference types is essential for writing efficient, bug-free code. If you’re looking to master crucial coding and system design concepts, check out the following resources on DesignGurus.io:

• Grokking the Coding Interview: Patterns for Coding Questions
• Grokking the System Design Interview (if you’re interested in how these design considerations play out at scale)

You can also find free tutorials and discussions on coding interviews, system design, and best practices on the DesignGurus.io YouTube channel. By understanding exactly when to use structs over classes, you’ll write more performant and predictable C# applications.