Community discussion forum

Error when using Method Extensions

• • Reply

  1 year ago

  by rajambal_j

  rajambal_j

  , India

  Joined 2 years ago
  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
  

  Report abuse
• • Reply

  1 year ago

  by rajambal_j

  rajambal_j

  , India

  Joined 2 years ago

  I found the solution.

  The issue is that the Object class contains a static method with 2 parameters of type Object. Since the .NET Framework first looks at the methods declared within the class, this one is used which is not possible to use on an instance.

   Greetz,

   Geert

  Report abuse