Yield

The yield keyword before a return statement greatly simplifies creating a Numerator to enable the use of the for each loop. For a collection to be traversed by a foreeach loop that collection must implement the IEnumerable Interface which has one function that returns an instance of INumerator, now from my previous post we saw that it's a bit involved however the Yield keyword greatly simplifies that.

Let's start with a person class.

class 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 IEnumerable<DayOfWeek> BirthWeekDays() {

        for (int i = 0; i < this.Age+2; i++)

            yield return Birthdate.AddYears(i).DayOfWeek;

    }

    public override string ToString() { return $"{Age} {FirstName} {LastName}"; }

}

now this "Person" class differs slightly in the sense that it has the BirthWeekDays function, this function returns an IEnumerable of the DayOfWeek type; in essence it just returns every day of the week since you where born, so if you where born on a Tuesday, that's where it would start.

so let's see how it goes.

class Program

{

    static void Main(string[] args)

    {

        var p = new Person {

            FirstName = "Pawel",

            LastName = "Ciucias",

            Birthdate = new DateTime(1984, 1, 31)

        };

        foreach(var wd in p.BirthWeekDays())

            Console.WriteLine(wd.ToString());

        Console.WriteLine(p.ToString());

    }

}

now our application just zips through and lists all of the birth weekdays our person had since birth until their next birthday.