Question

MyClass[] array; List<MyClass> list; 

What are the scenarios when one is preferable over the other? And why?

Answer 1

It is rare, in reality, that you would want to use an array. Definitely use a List<T> any time you want to add/remove data, since resizing arrays is expensive. If you know the data is fixed length, and you want to micro-optimise for some very specific reason (after benchmarking), then an array may be useful.

List<T> offers a lot more functionality than an array (although LINQ evens it up a bit), and is almost always the right choice. Except for params arguments, of course. ;-p

As a counter – List<T> is one-dimensional; where-as you have have rectangular (etc) arrays like int[,] or string[,,] – but there are other ways of modelling such data (if you need) in an object model.

See also:

• How/When to abandon the use of Arrays in c#.net?
• Arrays, What’s the point?

That said, I make a lot of use of arrays in my protobuf-net project; entirely for performance:

• it does a lot of bit-shifting, so a byte[] is pretty much essential for encoding;
• I use a local rolling byte[] buffer which I fill before sending down to the underlying stream (and v.v.); quicker than BufferedStream etc;
• it internally uses an array-based model of objects (Foo[] rather than List<Foo>), since the size is fixed once built, and needs to be very fast.

But this is definitely an exception; for general line-of-business processing, a List<T> wins every time.