Code Inspection: Non-accessed positional property (non-private accessibility)

C# 9 record syntax defines a bunch of members implicitly, including Equals()/GetHashCode()/ToString() implementations, properties corresponding to primary constructor parameters, and the Deconstruct() method.

Taking into account all these implicit definitions, JetBrains Rider reports positional properties of records that are never accessed.

  record Person(
    string Name,
    int Age, // non-accessed positional property
    object Tag
  );

  class SomeClass
  {
    public void PrintName()
    {
      var (name, _, tag) = GetPerson();
      Console.WriteLine(name);
    }

    public Person GetPerson() => new("Alex", 32, null);
  }

        

  record Person(
    string Name,
    object Tag
  );

  class SomeClass
  {
    public void PrintName()
    {
      var (name, tag) = GetPerson();
      Console.WriteLine(name);
    }

    public Person GetPerson() => new("Alex", null);
  }

        

To make removal of redundant positional members safe, the Remove unused property quick-fix (Alt+Enter) invokes the Safe Delete refactoring to support all record usage patterns. In the example above, JetBrains Rider recognizes indirect usages in all C# deconstruction forms and is able to remove the corresponding _ from such deconstructions.

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 positional member 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 positional member in one of the following ways:

The recommended way is to decorate the implicitly used positional member 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 positional member 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: 04 January 2022