Code inspection: Field can be made readonly (non-private accessibility)

Say you have decided to make a Person class, initialized only via the constructor, but with publicly available fields. You go ahead and implement the following:

public class Person
{
  public string Name;
  public int Age;
  public Person(string name, int age)
  {
    Name = name;
    Age = age;
  }
  public override string ToString() =>
    $"Name: {Name}, Age: {Age}";
}
        

Public Class Person
	Public Name As String
	Public Age As Integer
	Public Sub New(name As String, age As Integer)
		Me.Name = name
		Me.Age = age
	End Sub
	Public Overrides Function ToString() As String
		Return String.Format("Name: {0}, Age: {1}", Name, Age)
	End Function
End Class
        

If solution-wide inspection is enabled, JetBrains Rider can detect that the fields are only being assigned in the constructor and offers to create an additional safeguard: by marking them readonly, we get to ensure that neither this class nor its users will inadvertently assign new values to these fields.

For the solution-wide inspection to work, you need to enable at least one of the following:

Simplified global usage checking: select Show unused non-private type members when solution-wide analysis is off on the Editor | Inspection Settings page of JetBrains Rider settings Ctrl+Alt+S.
Solution-wide analysis: select Enable solution-wide analysis on the Editor | Inspection Settings page of JetBrains Rider settings Ctrl+Alt+S.

Note that even if the reported field has no direct usages in your solution, there could be cases where it is used indirectly — for example, via reflection — or it could just be designed as public API. In all those cases, you would want to suppress the usage-checking inspection for the field in one of the following ways:

The recommended way is to decorate the implicitly used field with a code annotation attribute. There are two attributes for this purpose: [UsedImplicitly] and [PublicAPI], which are functionally similar, but let you and your teammates understand how the field is actually used.
You can also suppress usage-checking inspections with any custom attribute. To do so, mark the definition of that attribute with the [MeansImplicitUse] attribute.
And finally, you can suppress a specific usage-checking inspection as any other code inspection with a suppression comment or a suppression attribute.

Last modified: 11 February 2024