Or: Unavailability of value comparison of objects in .NET, a technical or philosophical restriction?
I was working on unit tests and then a question came to me – why comparing objects by value is not provided out-of-the-box by the .NET Framework? We all (should) know that by default, comparing objects leads to a reference comparison, unless of course you override Equals() or implement operator == on your class.
But what if I want to compare two objects from a class provided by the Framework? That would be quite handy specially for unit tests. While we have System.Object.Equals() and System.Object.ReferenceEquals() working the very same way – reference comparison – we don’t find something like System.Object.ValueEquals().
Then I started having a discussion with a friend and colleague of mine the reasons for such functionality not existing in .NET.
Although I agree that the default option should be reference comparison, I don’t see any technical limitations for not having that implemented – Reflection could be the way to do it, going recursively down each property and checking if their values are equal.
So why not? Is it something related to the theory of object orientation or was it a mere technical decision?
Let’s take one of the classical examples of OO lessons: a Car class. In a Car, you have properties such as Color, Model, Category, etc. In real life, when two cars come out of production line, while you can’t say they are the same car, one would have no problem identifying they were built by the same method. Just compare each of their properties and you will end up knowing they are not the same car, but they share the same properties and were built the same way. They don’t share a reference equality, but value equality.
As far as I am concerned, OO does not provide a specific way or method to apply the property-by-property comparison, but there isn’t a prohibition on doing that as well.
However, providing such functionality could be an expensive trade-off, since gigantic objects with collections with millions of items could be compared. It would be possible, but sometimes not practical. But then not providing that for the developer’s discretion, or at least providing ways to ensure it could be safely used? Doesn’t seems right to me.
From my point of view, such functionality could be very useful and there is no true restriction that should be applied for having something like that provided by the Framework. As I said, my opinion is that not providing it is a technical decision, and not a philosophical restriction imposed by OO theory.
What do you think? I’d be glad to listen to other opinions!
