[Interest] Qt based Ordered Map container

[Mandeep Sandhu]

Hi All,

Sometime (almost 2 yrs!) back we had a discussion here about having a new
container type in Qt which would be like a QMap, except that it stored keys
in their insertion order. This was mostly inspired by a Python
data-structure - OrderedDict (
http://docs.python.org/library/collections.html#collections.OrderedDict).

Recently, I had some free time on hand and so though of implementing it
using existing Qt containers. Here's the code for it:
https://github.com/mandeepsandhu/qt-ordered-map

It's not a core container in itself as it uses existing Qt containers for
most of the implementation (much like the Python implementation).

For storing the data I use a QHash and for keeping the key (insertion)
order, I use a QLinkedList. The value stored in the hash, is actually a
pair - of the user provided value and a QLinkedList _iterator_ which points
to the item inserted in the linklist. This makes it quite easy and fast to
delete items from these 2 containers in constant time.

The performance of this container is similar to QHash except when you want
all the values from it, as that requires first fetching the keys from the
linklist and then using that to fetch the values from the hash table.

It provides a sub-set of QMap API, complete with const and non-const
iterators (you can use 'foreach' for iterating over all the values in their
insert order).

In case you want to use such a container, please try it out and let me know
your feedback.

Thanks,
-mandeep
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