Comments on: Comparing Ruby and C#: Equality

By: Andreas

Andreas — Sat, 20 Mar 2010 10:45:54 +0000

Just some comments:

The Colophon sample is somewhat unfortunate because the String case of
System.Console.WriteLine (Object.ReferenceEquals (obj0, obj1));
will deliver somesthing completely different from what somebody would expect after your post.

And the explanation for Equals() is problematic. Equals SHOULD deliver if two instances are – well – equal, NOT that they are the same reference. It is right that the default implementation works like that, but it SHOULD be overridden in subclasses to test for content equality.

By: Mario Carrion

Mario Carrion — Thu, 18 Mar 2010 22:15:45 +0000

@yoeri Fixed!
@doza You are absolutely right. Post updated.

By: doza

doza — Thu, 18 Mar 2010 07:57:34 +0000

Ruby doesn’t have weak typing, you probably meant dynamic

By: yoeri

yoeri — Thu, 18 Mar 2010 06:45:18 +0000

Hi, small typo … Ruby equal? line 11 should say b and a are different types, now it says b and c are different types.

grtz
y

By: Mario Carrion

Mario Carrion — Wed, 17 Mar 2010 20:09:21 +0000

I totally agree with you, overriding Equals() or == will change the meaning of the original method or operator. The idea of this post was to show the default implementations, explaining why would it be different is out the scope. Thanks for bringing this up, is important to tell this difference.

By: sukru

sukru — Wed, 17 Mar 2010 19:54:45 +0000

There is a small mixup in titles:
“Method equal?”
and “Operator equals (==)” are swapped i Ruby section.

Also while base C# object.Equals implementation is as you describe (reference for reference, bitwise for value), sub-classes are able to (and often do) implement value equality by overriding the method:

http://msdn.microsoft.com/en-us/library/bsc2ak47.aspx

Note that a derived type might override the Equals method to implement value equality. Value equality means the compared objects have the same value even though they have different binary representations. For example, consider two Decimal objects that represent the numbers 1.10 and 1.1000. The Decimal objects do not have bitwise equality because they have different binary representations to account for the different number of trailing zeroes. However, the objects have value equality because the numbers 1.10 and 1.1000 are considered equal for comparison purposes since the trailing zeroes are insignificant.