Using Large Lists

In an Outlook AddIn I'm working on, I use a list to grab all the messages in the current folder, then process them, then save them. First, I create a list of all messages, then I create another list from the list of messages, then finally I create a third list of messages that need to be moved. Essentially, they are all copies of each other, and I开发者_运维百科 made it this way to organize it. Would it increase performance if I used only one list? I thought lists were just references to the actual item.

Without seeing your code it is impossible to tell if you are creating copies of the list itself or copies of the reference to the list - the latter is preferable.

Another thing to consider is whether or not you could stream the messages from Outlook using an iterator block. By using a List<T> you are currently buffering the entire sequence of messages which means you must hold them all in memory, processing them one at a time. Streaming the messages would reduce the memory pressure on your application as you would only need to hold each message in memory long enough to process it.

Unless your lists contains 10 millions items or more, it should not be a problem.

Outlook seems to have a problem much smaller sized mailboxes, so I would say you are pretty much safe.