Comparer<T>.Default Property

Question

This question comes from this Little Wonders: Comparer<T>.Default . I am wondering what the author wrote in the line:

If the type you want to compare already implements IComparable<T> or if the type is System.Nullable<T> where T implements IComparable, there is a class in the System.Collections.Generic namespace called Comparer<T> which exposes a property called Default that will create a singleton that represents the default comparer for items of that type.

So for example :

I have a class :

class Foo : IComparable<Foo> { ... }
public class FooComparer : IComparer<Foo> { ... }

Comparer class implemented as public abstract class Comparer<T> : IComparer, IComparer<T> . My question is how Default property works overall , what it does and how it works?

Thanks

Answer 1

Comparer<T>.Default doesn't use your FooComparer class. It simply returns an instance of the internal class GenericComparer<T>.
This class has the constraint that T must implement IComparable<T> so it can simply delegate the calls to it Compare method to the Compare methods of the instances it gets passed.

Something like this:

internal class GenericComparer<T> : Comparer<T> where T : IComparable<T>
{
    public override int Compare(T x, T y)
    {
        if (x != null)
        {
            if (y != null)
                return x.CompareTo(y);
            return 1;
        }
        else
        {
            if (y != null)
                return -1;
            return 0;
        }
    }

    // ...
}