Question

I have simplified my code to this

 internal class Program
{
    private static void Main(string[] args)
    {
        Child d = new Child();
        int i = 100;
        d.AddToTotal(i);

        Console.ReadKey();
    }

    private class Parent
    {
        public virtual void AddToTotal(int x)
        {
            Console.WriteLine("Parent.AddToTotal(int)");
        }
    }

    private class Child : Parent
    {
        public override void AddToTotal(int number)
        {
            Console.WriteLine("Child.AddToTotal(int)");
        }

        public void AddToTotal(double currency)
        {
            Console.WriteLine("Child.AddToTotal(double)");
        }
    }
}

The issue is that this calls

public void AddToTotal(double currency)

although I am calling it with an int and it should be using

public override void AddToTotal(int number)

Using the parent returns the expected result.

 Parent d = new Child();
 int i = 100;
 d.AddToTotal(i);

Update:

Thanks to @Jan and @azyberezovsky for pointing me to the specification. I have added a virtual empty method to the base class to get around this for now.

Answer 1

A member lookup of a name N in a type T is processed as follows:

First, the set of all accessible members named N declared in T and the base types of T is constructed. Declarations that include an override modifier are excluded from the set. If no members named N exist and are accessible, then the lookup produces no match, and the following steps are not evaluated.

Thus when you use variable of Child type

Child d = new Child();
int i = 100;
d.AddToTotal(i);

method public override void AddToTotal(int number) is excluded from set, and we have only one method with name N left. Int is converted implicitly to double, so no errors occured.