ArrayList and List<object> - Not List<T> in C# [duplicate]

Question

I saw this reply from Jon on Initialize generic object with unknown type:

If you want a single collection to contain multiple unrelated types of values, however, you will have to use List<object>

I'm not comparing ArrayList vs List<>, but ArrayList vs List<object>, as both will be exposing elements of type object. What would be the benefit of using either one in this case?

EDIT: It's no concern for type safety here, since both class is exposing object as its item. One still needs to cast from object to the desired type. I'm more interested in anything other than type safety.

EDIT: Thanks Marc Gravell and Sean for the answer. Sorry, I can only pick 1 as answer, so I'll up vote both.

Answer 1

You'll be able to use the LINQ extension methods directly with List<object>, but not with ArrayList, unless you inject a Cast<object>() / OfType<object> (thanks to IEnumerable<object> vs IEnumerable). That's worth quite a bit, even if you don't need type safety etc.

The speed will be about the same; structs will still be boxed, etc - so there isn't much else to tell them apart. Except that I tend to see ArrayList as "oops, somebody is writing legacy code again..." ;-p

Answer 2

One big benefit to using List<object> is that these days most code is written to use the generic classes/interfaces. I suspect that these days most people would write a method that takes a IList<object> instead of an IList. Since ArrayList doesn't implement IList<object> you wouldn't be able to use an array list in these scenarios.

I tend to think of the non-generic classes/interfaces as legacy code and avoid them whenever possible.