Are List<> elements sequentially located in heap like array?

Question

I\'m learning C# and basically know the difference between arrays and Lists that the last is a generic and can dynamically grow but I\'m wondering:

Answer 1

Yes, elements in a List are stored contiguously, just like an array. A List actually uses arrays internally, but that is an implementation detail that you shouldn't really need to be concerned with.

Of course, in order to get the correct impression from that statement, you also have to understand a bit about memory management in .NET. Namely, the difference between value types and reference types, and how objects of those types are stored. Value types will be stored in contiguous memory. With reference types, the references will be stored in contiguous memory, but not the instances themselves.

The advantage of using a List is that the logic inside of the class handles allocating and managing the items for you. You can add elements anywhere, remove elements from anywhere, and grow the entire size of the collection without having to do any extra work. This is, of course, also what makes a List slightly slower than an array. If any reallocation has to happen in order to comply with your request, there'll be a performance hit as a new, larger-sized array is allocated and the elements are copied to it. But it won't be any slower than if you wrote the code to do it manually with a raw array.

If your length requirement is fixed (i.e., you never need to grow/expand the total capacity of the array), you can go ahead and use a raw array. It might even be marginally faster than a List because it avoids the extra overhead and indirection (although that is subject to being optimized out by the JIT compiler).

If you need to be able to dynamically resize the collection, or you need any of the other features provided by the List class, just use a List. The performance difference will be virtually imperceptible.