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[p2-dev] Review wanted. Simplifying the IQueryResult/IQuery API

I've done some work to simplify the IQueryResult/IQuery API further. Once Ian's patch came in yesterday, it was possible for me to move forward on two things that I wanted to do for some time.

1. Establish a clear separation of concern between query processing and the processing of a query result.
This item was very easy to do now. The work entailed three things:

- Removal of the addAll() method from the IQueryResult
- Make IQuery.perform() return an IQueryResult instead of a Collector
- Remove the Collector argument from the IQuery.perform()

Now the IQuery looks like something that produces a read-only result. This is very much in line with how the QL is designed and will make the integration that I'd like to do as the next step very easy. It will also vouch for some furhter performance improvements since we can write very streamlined IQueryResults for different purposes.

2. Avoid use of collections as long as possible.
A query can produce a huge result. Huge results take up a lot of memory. Consequently, a good 'query' design should not encourage the use of collections unless they are absolutely necessary. I did the following to address this:

- Removed the 'size()' from IQueryResult
- Removed the 'toCollection()' methods from the IQueryResult

The toCollection() would always create a copy of the Collector collection. In many cases, this collection was obtained only to pass as an argument to the constructor of another collection. In some cases, the collection was only obtain in order to get the size. Now, when neither method is there, it's less intuitive to use a collection and more intuitive to use an iterator. This is a good thing since the query result may be very large. In case of QL, it may not contain a collection in the first place.

I just submitted a new attachment to https://bugs.eclipse.org/bugs/show_bug.cgi?id=298023 because the other one went stale almost immediately. Not surprising since it touches a lot of files. But it does show that a review is somewhat urgent. So please, if you could take a look and give me a go ahead, or a reason not to, I'd appreciate it.

Thomas Hallgren