Anonymous Methods in C# 2.0

Provided by Dave Juth, Senior Systems Architect

Anonymous methods, a new feature in C# 2.0, allow you to write more concise code and avoid some of the hassles of hooking up event handlers for trivial operations. Instead of declaring a method that can be accessed by a delegate, you can now write the method’s code inline.

The following example illustrates two anonymous methods, one to sort a list of people and one to loop through and output each member of the list:

using System;

using System.Collections.Generic;

using System.Text;

 

namespace AnonymousMethodsConsole

{

    public class Program

    {

        static void Main(string[] args)

        {

            List<Person> people = new List<Person>();

 

            Person teacher = new Person();

            teacher.LastName = "Smith";

            teacher.FirstName = "Joe";

            teacher.DOB = new DateTime(1959, 12, 20);

 

            people.Add(teacher);

 

            Person doctor = new Person();

            doctor.LastName = "Williams";

            doctor.FirstName = "Mary";

            doctor.DOB = new DateTime(1973, 5, 5);

 

            people.Add(doctor);

 

            Person lawyer = new Person();

            lawyer.LastName = "Jones";

            lawyer.FirstName = "Tom";

            lawyer.DOB = new DateTime(1966, 3, 15);

 

            people.Add(lawyer);

 

            people.Sort(delegate(Person p1, Person p2) {return Comparer<DateTime>.Default.Compare(p1.DOB, p2.DOB);});

 

            people.ForEach(delegate(Person p) { Console.WriteLine(p.FirstName + " " + p.LastName + " " + p.DOB.ToShortDateString()); });

 

            Console.ReadKey();

        }

    }

 

    public class Person

    {

        public string LastName = string.Empty;

        public string FirstName = string.Empty;

        public DateTime DOB;

 

        public Person()

        {           

        }

    }

}

The first anonymous method is a custom sort for a person’s date of birth, and it sorts the collection of people by the DOB property:

people.Sort(delegate(Person p1, Person p2) {return Comparer<DateTime>.Default.Compare(p1.DOB, p2.DOB);});

 The second prints out the sorted collection of people using an anonymous method instead of a typical foreach loop.

people.ForEach(delegate(Person p) { Console.WriteLine(p.FirstName + " " + p.LastName + " " + p.DOB.ToShortDateString()); });