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Answer: A struct is a value type: assigning or passing it copies the data. A class is a reference type: copies share one object.

public readonly struct Point(double x, double y) {
  public double X { get; } = x;
  public double Y { get; } = y;
}

var a = new Point(1, 2);
var b = a;  // independent copy

readonly struct

Because structs have value semantics, Microsoft recommends making them immutable. If you don't initialize all fields in a struct, the compiler adds code to the constructor that initializes those fields to the default value. (S1)

When a class fits better

• The type has complex behavior or manages mutable state.
• You need inheritance.
• Instances represent a shared identity, and all references should see the same changes.

Gotchas

• Large structs are expensive to copy.
• Boxing a struct to object or an interface allocates.
• For information about ref struct and readonly ref struct types, see the ref structure types article. (S1)

Claims

• id: C1 claim: A struct type is a value type. source: S1 evidence: "A structure type (or struct type) is a value type that can encapsulate data"
• id: C2 claim: Because structs have value semantics, immutable structs are recommended. source: S1 evidence: "Because structure types have value semantics, we recommend you define immutable structure types."
• id: C3 claim: All data members of a readonly struct must be read-only. source: S1 evidence: "All data members of a readonly struct must be read-only as follows:"
• id: C4 claim: Classes fit types with complex behavior or mutable state. source: S2 evidence: "The type has complex behavior or manages mutable state."
• id: C5 claim: Classes support inheritance. source: S2 evidence: "Classes support inheritance."

Sources

• [S1] Structure types - C# reference. Microsoft Learn (.NET docs). https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/struct . License: CC BY 4.0 (dotnet/docs). Accessed 2026-11-04.
• [S2] C# classes - C#. Microsoft Learn (.NET docs). https://learn.microsoft.com/en-us/dotnet/csharp/fundamentals/types/classes . License: CC BY 4.0 (dotnet/docs). Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_jcafahmw,
  author = {{iinventedlight}},
  title = {{C\# structs vs classes}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/csharp-structs/},
  note = {Permanent ID iil:note:jcafahmw. License: CC-BY-4.0.},
}

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