Code inspection: Unused parameter (non-private accessibility)

This inspection reports parameters that are declared in an interface, abstract, or virtual method, but are not used in the method itself or any of the methods that inherit from it.

The presence of an unused parameter can be misleading to other developers. It could also be indicative of an error where the parameter was intended to be used, but was inadvertently overlooked, possibly leading to unexpected behavior or bugs in the application.

In the below example, the users of the ITestable interface would probably not check implementations of the PrintString method because its name and signature seem self-explanatory — they would expect it to print the string passed by the argument. So the fact that the method could print a constant string might be an unexpected behavior.

        
public interface ITestable
{
    public void PrintString(string str){}
}

public class Testable : ITestable
{
    public void PrintString(string str)
    {
        Console.WriteLine("Hello world");
    }
}

public class Test
{
    public Test(ITestable sample)
    {
        sample.PrintString("test this");
    }
}

    

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 parameter 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 parameter in one of the following ways:

The recommended way is to decorate the implicitly used parameter 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 parameter 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: 29 May 2024