Error when using Method Extensions 1

[GeertVerhoeven]

Hi all,

I'm practicing with the C# 3.0 Language Enhancements and get stuck with the following issue on method extensions.

The goal is to write an Equals method for the datetime type which accepts an additional parameter indicating until which level the comparison must be done (Year / Month / Day).

The code works when I use the static method directly but when I use the extension method syntax, it doesn't work.

Here is my code:

using System;


namespace Extension_Methods
{
    class Program
    {
        static void Main(string[] args)
        {
            DateTime date = new DateTime(2008, 1, 1);
            DateTime date2 = new DateTime(2008, 1, 2);

            // Code below works 
            Console.WriteLine(DateTimeUtils.Equals(date, date2, DatePrecision.Month));

            // ERROR on line below:
            // Member 'object.Equals(object, object)' cannot be accessed with an instance reference; qualify it with a type name instead
            Console.WriteLine(date.Equals(date2, DatePrecision.Month));

            Console.WriteLine("Press any key to continue.");
            Console.ReadKey();
        }
    }

    public static class DateTimeUtils
    {
        public static bool Equals(this DateTime date, DateTime comparisonDate, DatePrecision precision)
        {
            switch (precision)
            {
                case DatePrecision.Year:
                    return date.Year.Equals(comparisonDate.Year);

                case DatePrecision.Month:
                    return  date.Year.Equals(comparisonDate.Year) && 
                            date.Month.Equals(comparisonDate.Month);                    

                case DatePrecision.Day:
                    return date.Year.Equals(comparisonDate.Year) &&
                            date.Month.Equals(comparisonDate.Month) &&
                            date.Day.Equals(comparisonDate.Day);

                default:
                    return false;
            }
        }
    }

    public enum DatePrecision
    {
        Year,
        Month,
        Day
    }
}

I hope someone can help me with this.

Greetz,

Geert


Geert Verhoeven
Consultant @ Ausy Belgium

My Personal Blog

 

[jel]

My guess would be:
there already exists an overload Object.Equals(Object, Object), and that one is indeed a static - it cannot be accessed with an instance reference.
As DateTime and emums all are objects, your method has the same signature as the existing one.
Have you tried changing the name of your method to something like 'EqualsByPrecision'?

 

[GeertVerhoeven]

Thanks Jel.

I think that will be the reason. It does work when I give the method a different name.

I've found some extra info as well:

http://www.msdner.com/dev-archive/161/153-1016-1615497.shtm

Greetz,

Geert

Geert Verhoeven
Consultant @ Ausy Belgium

My Personal Blog