Asp .Net MVC Viewmodel should be class or struct?

I have just been thinking about the concept of view model object we create in asp.net MVC. Our purpose is to instantiate it and pass it from controller to view and view read it and display the data.

Those view model are usually instantiated through constructor. We won't need to initialize the members, we may not need to redefine/override parameterless constructor and we don't need inheritance feature there.

So, why don't we开发者_JAVA百科 use struct type for our view model instead of class. It will enhance the performance.

You take "it will enhance the performance" as a given, but are you really sure about this? Structs perform better than classes in very specific circumstances. I'm generalizing for simplicity, but the scenarios chiefly are:

• They're immutable.
• They're small, e.g. usually no more than 3 - 4 fields.
• You're generating tons (often millions or more) of them over an extremely short time span.
• You're working with them in tight loops.
• The code paths that they travel through are optimized for those specific structs and do not perform boxing / unboxing operations.

There are others, but that's just off the top of my head. And even then, we're talking about often minuscule performance gains. As in microseconds minuscule.

Even if you can guarantee that your view models are immutable and tiny, the other conditions don't hold. Assuming one view model per request, your web server is not going to handle millions of requests per second. Furthermore, the MVC framework does not work with these in tight loops and does not contain code paths optimized for this particular struct. The MVC framework will end up performing tons of boxing / unboxing operations on your value types as a result.

Bottom line - don't micro-optimize or over-engineer your solution. Classes are just fine. And when optimization is concerned, always measure to make sure you're devoting your time to a worthwhile venture. Don't bother with trivialities when there are bigger fish to fry.

use a class. some view models require constructors, converters and maybe more functionality, why limit to struct? (like if you have EF4 objects and you need to make POCO out of them...)