# Is ArrayLists so slow that it is doomed to kill performance in Unity?

I was reading Which Kind Of Array Or Collection Should I Use?

The document states to use list for the most performance.

"...They are the fastest array in unity. For this reason, built-in arrays are the best choice if you need the fastest performance possible from your code (for example, if you're targeting iPhone)...performs significantly faster than ArrayList."

I am inclined to use list besides performance issues as well because...

But it got me to wonder, since everyone seems to favor to make a degrading statement about ArrayLists, is ArrayLists that horrible? If so why does it even exist? Is it more of trace of supposedly deprecated codes?

Yes, ArrayLists are slow (relative). ArrayLists were part of the .NET framework before .NET 2.0 was released. .NET 2.0 brought us generics which are better for 'generic' collections. More specifically, ArrayLists' .Add method accepts objects causing boxing, whereas, a List<T> takes a predetermined type.. therefore, increasing performance.
For all practical purposes, the functionality of ArrayList in the current .NET Framework is for backwards compatibility with project using .NET Framework 1.0 / 1.1.