IComparable

IComparable<T> defines a generic function that facilitates the sorting of instances of the type that implements it. For example if we had our person class and implemented the "CompareTo" function;

class Person : IComparable<Person>

{

    public string FirstName { get; set; }

    public string LastName { get; set; }

    public DateTime BirthDate { get; set; }

    public int Age

    {

        get

        {

            var today = DateTime.Today;

            var age = today.Year - BirthDate.Year;

            return BirthDate > today.AddYears(-age) ? --age : age;

        }

    }

    public override string ToString()

    {

        return $"{Age}) {FirstName} {LastName}";

    }

    public int CompareTo(Person other)

    {

        return Age - other.Age;

    }

}

we see that the "CompareTo" function has three types of results,

• a negative int: which means that the other person is has a higher age and will be to the right of the current person
• a zero: which mean that the two people are of equal age and will be next to each other
• a positive int: meaning that the other person is younger and will be to the left of the current Person.

Now let's demonstrate the IComparable interface in action

using System;

using System.Collections.Generic;

namespace pc.IComparable

{

    class Person : IComparable<Person>

    {

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public DateTime BirthDate { get; set; }

        public int Age

        {

            get

            {

                var today = DateTime.Today;

                var age = today.Year - BirthDate.Year;

                return BirthDate > today.AddYears(-age) ? --age : age;

            }

        }

        public override string ToString()

        {

            return $"{Age}) {FirstName} {LastName}";

        }

        public int CompareTo(Person other)

        {

            return Age - other.Age;

        }

    }

class Program

{

    static void Main(string[] args)

    {

        var p1 = new Person { FirstName = "Tomek", LastName = "Chooch",

            BirthDate = new DateTime(1988, 8, 28) };

        var p2 = new Person { FirstName = "Pawel", LastName = "Chooch",

            BirthDate = new DateTime(1984, 6, 28) };

        var p3 = new Person { FirstName = "Marin", LastName = "Smartz",

            BirthDate = new DateTime(1983, 11, 3) };

        var p4 = new Person { FirstName = "Magda", LastName = "Chooch",

            BirthDate = new DateTime(1984, 1, 31) };

        var p5 = new Person { FirstName = "Jakeb", LastName = "Tywonk",

            BirthDate = new DateTime(1988, 5, 4) };

        var p6 = new Person { FirstName = "Ivanp", LastName = "endasd",

            BirthDate = new DateTime(1986, 3, 3) };

        var p7 = new Person { FirstName = "Jakes", LastName = "gadicd",

            BirthDate = new DateTime(1986, 3, 2) };

        var p8 = new Person { FirstName = "Bober", LastName = "asdasd",

            BirthDate = new DateTime(1986, 3, 1) };

        var ppl = new List<Person>(new Person[] { p1, p2, p3, p4, p5, p6, p7, p8 });

        ppl.Sort();

        foreach (var p in ppl)

            Console.WriteLine(p.ToString());

    }

}

As you can see we create 8 instances of our person class put them into an array, sort it and then output them in their sorted by age.