S3466 — Optional parameters should be passed to "base" calls

Why is this an issue?

When optional parameter values are not passed to base method calls, the value passed in by the caller is ignored. This can cause the function to behave differently than expected, leading to errors and making the code difficult to debug.

How to fix it

Code examples

Noncompliant code example

public class BaseClass
{
    public virtual void MyMethod(int i = 1)
    {
        Console.WriteLine(i);
    }
}

public class DerivedClass : BaseClass
{
    public override void MyMethod(int i = 1)
    {
        // ...
        base.MyMethod(); // Noncompliant: caller's value is ignored
    }

    static int Main(string[] args)
    {
        DerivedClass dc = new DerivedClass();
        dc.MyMethod(12);  // prints 1
    }
}

Compliant solution

public class BaseClass
{
    public virtual void MyMethod(int i = 1)
    {
        Console.WriteLine(i);
    }
}

public class DerivedClass : BaseClass
{
    public override void MyMethod(int i = 1)
    {
        // ...
        base.MyMethod(i);
    }

    static int Main(string[] args)
    {
        DerivedClass dc = new DerivedClass();
        dc.MyMethod(12);  // prints 12
    }
}

Resources

Documentation

Microsoft Learn - Optional Arguments