c# - What's Wrong with an ArrayList?

Question

Recently I asked a question on SO that had mentioned the possible use of an c# ArrayList for a solution. A comment was made that using an arraylist is bad. I would like to more about this. I have never heard this statement before about arraylists. could sombody bring me up to speed on the possible performance problems with using arraylists

c#. .net-2

Answer 1

The main problem with ArrayList is that is uses object - it means you have to cast to and from whatever you are encapsulating. It is a remnant of the days before generics and is probably around for backwards compatibility only.

You do not have the type safety with ArrayList that you have with a generic list. The performance issue is in the need to cast objects back to the original (or have implicit boxing happen).

Implicit boxing will happen whenever you use a value type - it will be boxed when put into the ArrayList and unboxed when referenced.

The issue is not just that of performance, but also of readablity and correctness. Since generics came in, this object has become obsolete and would only be needed in .NET 1.0/1.1 code.