Anonymous IComparer implementation

Question

Is it possible to define an anonymous implementation of IComparer?

I believe Java allows anonymous classes to be defined inline - does C#?

Looking at this code I

Answer 1

C# does not allow implementing interfaces using anonymous inner classes inline, unlike Java. For simple comparisons (i.e. comparing on a single key), there is a better way to do this in C#. You can simply use the .OrderBy() method and pass in a lambda expression specifying the key.

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;


namespace Test{
    public class Test{
        public static void Main(){
            IList<int> mylist = new List<int>();
            for(int i=0; i<10; i++) mylist.Add(i);
            var sorted = mylist.OrderBy( x => -x );
            foreach(int x in sorted)
                Console.WriteLine(x);
        }
    }
}

Answer 2

Even though you can't create anonymous classes that implement interfaces, you can usually use the Comparison Delegate instead of the IComparer Interface in most cases (like sorting, etc.):

Array.Sort(arr, (x, y) => 1);

Also there are some built-in implementations of IComparer like the Comparer Class or the StringComparer Class...

Answer 3

Take a look at these 2 SO questions, they tackle essentially the same problem

Use of Distinct with list of Custom Object

Wrap a delegate in an IEqualityComparer

If you go this way, you should pay special attention to Slaks' comments and Dan Tao's answer about the hashcode implementation

Answer 4

No, C# does not currently allow inline interface implementations; although it does allow you to create delegates inline through lambda expressions and anonymous methods.

In your case, I would suggest using a ProjectionComparer that makes it easy to use this feature, such as the one listed here.

Answer 5

Array.Sort(arrayName, (x,y) => string.Compare(x.Name,y.Name,StringComparison.CurrentCulture));

Answer 6

No, this is not possible. However, you can get the default implementation of IComparer<TKey> by Comparer<TKey>.Default. Otherwise you'll need to create a parameterized implementation and use an instance of that.