The World According to Nick
My take on Software, Technology, Politics, and anything else I feel like talking about.
Tuesday, March 30, 2004

C# FAQ: Object.Equals vs. operator == 

When should I use == and when should I use Equals? I actually didn't know this little tidbit... and my first reaction on reading about it was Ewwwwww... Here is the relevant portion:

The main difference between the two is polymorphism. Operators are overloaded, not overridden, which means that unless the compiler knows to call the more specific version, it'll just call the identity version. To illustrate that, here's an example:

using System;

public class Test
{
   static void Main()
   {
      // Create two equal but distinct strings
      string a = new string(new char[] {'h', 'e', 'l', 'l', 'o'});
      string b = new string(new char[] {'h', 'e', 'l', 'l', 'o'});

      Console.WriteLine (a==b);
      Console.WriteLine (a.Equals(b));

      // Now let's see what happens with the same tests but
      // with variables of type object
      object c = a;
      object d = b;

      Console.WriteLine (c==d);
      Console.WriteLine (c.Equals(d));
   }
}

The results are:

True
True
False
True

The third line is False because the compiler can only call the non-overloaded version of == as it doesn't know that the contents of c and d are both string references. As they are references to different strings, the identity operator returns false.


One more time... just for effect... Ewwwwww.

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Name: Nick
Home: Wauwatosa, WI, United States

I'm a Software Consultant in the Milwaukee area. Among various geeky pursuits, I'm also an amateur triathlete, and enjoy rock climbing. I also like to think I'm a political pundit.


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