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Monday, October 12, 2009

String =”” vs String.Empty

Here's a curious program fragment:

object obj = "Int32";
string str1 = "Int32";
string str2 = typeof(int).Name;
Console.WriteLine(obj == str1); // true
Console.WriteLine(str1 == str2); // true
Console.WriteLine(obj == str2); // false !?

Surely if A equals B, and B equals C, then A equals C; that's the transitive property of equality. It appears to have been thoroughly violated here.

Well, first off, though the transitive property is desirable, this is just one of many situations in which equality is intransitive in C#. You shouldn't rely upon transitivity in general, though of course there are many specific cases where it is valid. As an exercise, you might want to see how many other intransitivities you can come up with. Post 'em in the comments; I'd love to see what obscure ones you can come up with. (Incidentally, one of the interview questions I got when applying for this team was to invent a performant algorithm for determining intransitivities in a simplified version of the 'better method' algorithm.) Continue

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