C# Extension methods explained

Vegetables

Apple

SOLID code

public void myfunc()
{
    int myInt = 0;
    string myString = "y";
    string[] myStrings = {myString, "janaganamana", "me", "you" };

List<int> intList = new List<int> { myInt, 5,6,7 };

    Dictionary<string, int> myDict = new Dictionary<string, int> {
                                    { myString, myInt },
                                    { "janaganamana", 5 },
                                    { "me", 6 },
                                    { "you", 7 }
                        };
}

The above code may be very clear as a simple data types and initialization of same

Now if I have two classes

public class Individual
{
public string FirstName{get;set;}
public decimal pocketmoney{get;set;}

}
public class Friends
{
public List<Individual> Group { get; set; }
}

we can initialize

Friends myfiends = new Friends
{
    Group = new List<Individual> {
    new Individual {FirstName = "john", pocketmoney = 555M},
    new Individual {FirstName = "rama", pocketmoney = 65M},
    new Individual {FirstName = "king", pocketmoney = 77M}
}
};

That part is no brainer.

Now Let us use an extension method as explained earlier

http://www.janaganamana.net/onedefault.aspx?bid=780
1) ~~Extension methods need to be defined at a top level namespace.~~
2) class name does not matter much
3) parameter has "this" with one argument

namespace mynamespace
{
public static class MyExtensionMethods
{

        public static decimal TotalInvestment(this Friends allfriends)
        {
            decimal total = 0;
            foreach (Individual boy in allfriends.Group)
            {
                total += boy.pocketmoney;
            }
            return total;
        }
    }
}

Now you can call it as it it is a method of our friends class( notice"this Friends") above

decimal weHave = myfiends.TotalInvestment();decimal weHave = myfiends.TotalInvestment();

Update the Friends class as below.

public class Friends : IEnumerable<Individual>
{
    public List<Individual> Group { get; set; }
    public IEnumerator<Individual> GetEnumerator()
    {
        return Group.GetEnumerator();
    }
    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}

public static class MyExtensionMethods
{
    public static decimal TotalInvestment(this IEnumerable<Individual> allfriends)
    {
        decimal total = 0;
        foreach (Individual boy in allfriends)
        {
            total += boy.pocketmoney;
        }
        return total;
    }

    public static IEnumerable<Individual> FilterByRichToday(
            this IEnumerable<Individual> inds, int atLeast)
    {

        foreach (Individual ind in inds)
        {
            if (ind.pocketmoney > atLeast)
            {
                yield return ind;
            }
        }
    }
}
Now we can call as below ..
decimal weHaveAlmost = myfiends.FilterByRichToday(1000).TotalInvestment();

Notice ,, using extension methods, we did iteration inside our object also filteration where needed.