Structs (struct vs class)

A struct looks almost identical to a class, but there's one profound difference: a struct is a value type . It's copied when you assign or pass it, instead of shared by reference. Understanding value vs reference semantics is one of the most important things you'll learn in C# — it explains a whole category of "why did that change?!" bugs.

Learn Structs (struct vs class) in our free C# course — a beginner-friendly interactive lesson with worked examples, a practice exercise and a quick recall.

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Imagine handing a colleague a document. With a class , you share a single Google Doc — they edit it and your copy changes too, because it's the same document. With a struct , you photocopy the document and hand them the copy — they can scribble all over it and your original is untouched. That photocopy-on-handover behaviour is exactly what "value type" means.

1. Declaring a Struct

A struct can hold fields, a constructor, properties and methods — syntactically it's nearly a class. It's ideal for small bundles of data that represent a single value, like a 2D point. The classic example is Point : two coordinates plus a little behaviour.

2. Value vs Reference Semantics

This is the whole point of the lesson. When you assign a struct to a new variable, you get an independent copy — change one and the other is unaffected. When you assign a class , both variables point at the same object — change one and you change "both". Run this side-by-side comparison and let it sink in.

Your turn — complete a temperature struct by writing a computed property.

3. readonly Structs

Mutable structs are a known foot-gun: because they copy so freely, a "change" you make might land on a copy you didn't mean to touch. The modern best practice is to make structs readonly so they're immutable — operations return a new value instead of mutating in place. This removes the surprise entirely.

4. record struct

If you want value-copy semantics and the free value equality, ToString() , and deconstruction of a record, use a record struct . A readonly record struct is the ideal small immutable value type — it's exactly what types like Vector or Color should be.

These lines build and use a struct, but they're scrambled. Order them so the program compiles and prints the area.

Fields, then constructor, then methods make up the struct body; you must construct r before calling Area() on it.

1 — b is a copy, so changing b.N leaves a.N at 1.

5 — a and b reference the same object, so the change is shared.

True — record structs get generated value equality.

Build a small immutable value type that represents a colour and can print itself as a hex string. This is a textbook real-world use of a readonly struct .

Practice quiz

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