Unused Method Parameter

csharp.unused_method_parameter

Severity

low

Remediation Complexity

medium

Remediation Risk

low

Remediation Effort

medium

Resource

Code Smell

Language

CSharp

Description

Reports method parameters that are never referenced in the method body. A parameter the method does not use is misleading: callers must still pass a value the method silently ignores.

Rationale

An unused parameter is a maintenance trap. It implies the value matters when it does not, and it lingers after a refactor that removed the only use. Methods whose signature is fixed by an external contract are excluded — override, virtual, abstract and partial methods, the canonical event-handler shape (object sender, EventArgs e), single-object-parameter BCL callback shapes such as TimerCallback’s `(object state), and the ASP.NET Core hosting convention methods (ConfigureServices, ConfigureContainer, Configure on a Startup class) — because there an unused parameter is required, not a defect. out/ref parameters and parameter arrays are also exempt: their value flows out through the binding or is contract-driven. A read as the governing subject of a switch expression or through a null-conditional invocation chain (handler?.Invoke(…)) also counts as a usage.

public class Service
{
    public int Add(int a, int b)
    {
        return a + b;               // OK — both used
    }

    public int First(int a, int b) // FLAW on b — never read
    {
        return a;
    }

    public virtual void Hook(int ctx) { }          // OK — virtual contract

    public void OnClick(object sender, EventArgs e) // OK — event-handler shape
    {
        Console.WriteLine("clicked");
    }

    public void OnTick(object state) { }            // OK — single-object callback shape

    private string DefaultMessageFor(int statusCode) // OK — switch expression subject
    {
        return statusCode switch
        {
            400 => "Bad request",
            _ => null
        };
    }

    public void Notify(EventHandler handler)        // OK — null-conditional invocation
    {
        handler?.Invoke(this, EventArgs.Empty);
    }
}

public class Startup
{
    public void ConfigureServices(IServiceCollection services) { } // OK — startup convention
}

Remediation

Remove the parameter and update every call site, or use it if it was meant to participate in the computation. When the signature is mandated by an interface or delegate that this rule did not detect, keep the parameter.

References

Methods