Question

I’m using the NumericComparer code located here. It’s very easy to add it to a project: NumericComparer

I have a List of strings with numbers in them and my code is simply this: myList.Sort(new NumericComparer());

The error I am getting is this:

cannot convert from ‘ns.NumericComparer’ to ‘System.Collections.Generic.IComparer’

Any ideas why?

Answer 1

It looks like the Sort method is expecting an implementation of IComparer<T> — generic, with a type parameter, whereas NumericComparer implements the non-generic IComparer interface.

So, if your list is, say a List<decimal>, you need to supply an IComparer<decimal>.

You should be able to quickly put together a class that leverages NumericComparer:

public class GenericNumericComparer<T> : IComparer<T>
{
    private static readonly NumericComparer _innerComparer = new NumericComparer();

    public int Compare(T x, T y)
    {
        return _innerComparer.Compare(x, y); // I'm guessing this is how NumericComparer works
    }
}

So now you can call myList.Sort(new GenericNumericComparer<decimal>());

(Note you can actually call your generic class NumericComparer too — it is distinguished by the type parameter. I added “Generic” here for clarity.)