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Answer: A C# property looks like a field to callers but runs get and set (or init) accessors. Unlike fields, properties are not variables, so they cannot be passed as ref or out.

public class Person {
  public required string FirstName { get; init; }
  public string LastName { get; private set; } = "";
  public string Name => $"{FirstName} {LastName}";   // computed
}

• Name has no backing field and is computed on each read.

Custom accessors

private int _age;
public int Age {
  get => _age;
  set {
    if (value < 0) throw new ArgumentOutOfRangeException(nameof(value));
    _age = value;
    AgeChanged?.Invoke(this, EventArgs.Empty);
  }
}

A get accessor must return or throw.

Claims

• id: C1 claim: The Name property is computed with no backing field. source: S1 evidence: "The Name property is a computed property. There's no backing field for Name."
• id: C2 claim: Simple properties can be auto-implemented. source: S1 evidence: "can be implemented either as expression body definitions or as automatically implemented properties."
• id: C3 claim: You can't pass a property as a ref or out parameter. source: S2 evidence: "Therefore, you can't pass a property as a ref or out parameter."
• id: C4 claim: Properties can take an action when data changes, such as raising an event. source: S2 evidence: "They can take an action when data is changed, such as raising an event"

Sources

• [S1] Properties - C#. Microsoft Learn (.NET docs). https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/properties . License: CC BY 4.0 (dotnet/docs). Accessed 2026-11-04.
• [S2] Using Properties - C#. Microsoft Learn (.NET docs). https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/using-properties . 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_b4zntcnj,
  author = {{iinventedlight}},
  title = {{C\# properties}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/csharp-properties/},
  note = {Permanent ID iil:note:b4zntcnj. License: CC-BY-4.0.},
}

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