Re: ArrayLists instead of List (for some things)

On 3 November 2017 at 03:26, Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:
> On 2 November 2017 at 22:22, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> wrote:
>> Maybe, but the new implementation is not going to do well with places
>> where we perform lcons(). Probably many of those places could be
>> changed to lappend(), but I bet there's plenty that need prepend.
>
> Yeah, and it's IMO significant that pretty much every nontrivial
> system with ADTs offers multiple implementations of list data
> structures, often wrapped with a common API.
>
> Java's Collections, the STL, you name it.

I've never really looked at much Java, but I've done quite a bit of
dotnet stuff in my time and they have a common interface ICollection
and various data structures that implement that interface. Which is
implemented by a bunch of classes, something like:

ConcurrentDictionary (hash table)
Dictionary (hash table)
HashSet (hash table)
LinkedList (some kinda linked list)
List (Arrays, probably)
SortedDictionary (bst, I think)
SortedList (no idea, perhaps a btree)
SortedSet
Bag (no idea, but does not care about any order)

Probably there are more, but the point is that they obviously don't
believe there's a one-size-fits-all type. I don't think we should do
that either. However, I've proved nothing on the performance front
yet, so that should probably be my next step.

--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services