Why is ReadOnlySpan<char> overload is chosen over string when inheritance is involved? even when the argument is string?

[fitdev]

Consider this code:

public class C {
    public virtual bool M(string? input) {
        return true;
    }
}

public abstract class D : C {
    public override bool M(string? input) {
        return base.M(input);
    }
    
    public abstract bool M(ReadOnlySpan<char> input);
}

public static class Test {
 
    public static void Run(D d) {
      var teststring = "Blah";
      d.M(teststring);  
    }
    
}

Question: why in the Test.Run routine D.M(ReadOnlySpan<char> input) is chosen over D.M(string? input) even though the argument passed is explicitly typed as string, i.e. var teststring = "Blah";

[svick]

why in the Test.Run routine D.M(ReadOnlySpan<char> input) is chosen over D.M(string? input)

What is happening here is that D.M(ReadOnlySpan<char>) is chosen over C.M(string?), because methods from derived classes are considered before methods from base classes. And, for the purposes of overload resolution, D.M(string?) does not exist.

[fitdev]

Thank you for a quick reply. I figured it may have something to do with inheritance. Is there a way to explicitly call the method I want without resorting to renaming it?

[PathogenDavid]

If you cast d to C it will call M(string). IE: ((C)d).M(teststring);