Very nice!  Just don't let it feature creep to Mode() or Median() ;)

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<br>I kinda miss being able to do perl-isms like get the -1'th entry in an array to get the last item - $a[-1] - it'd be kinda nice if there were indexers allowing such things in the Power Collections, but very low priority of course :)

I like the functionality, but part of me thinks that 1) These should be properties or 2) They should be named GetFirst() and GetLast().

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<br>I only suggest properties if your tree structure keeps references to the left-most and right-most nodes, so the property could have constant-time lookup.  Otherwise, I believe that these should remain methods...It's just that First() seems like a weird name for a method.

I am with Matthew

+1 for properties.

Good feedback. Looking at the design guidelines, it states that method should be named with a verb. So I agree, GetFirst() is to be preferred over First().

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<br>Should they be properties? That's not quite as clear cut. They aren't constant time, but take O(log N) to compute. So I think I agree with Matthew -- method is better than property in that case.

A OrderedSet is a container that is optimized for fast associative lookup. Items are matched using equals(). When an item is inserted into a OrderedSet, it is stored in a data structure that allows the item to be found very quickly. Within the data structure, the items are ordered according to a comparator object. By default, the comparator is a HashComparator that orders objects based on their hash value. The OrderedSet class supports the full range of generic set algorithms such as union() and intersection() in a user-friendly manner. Duplicates are not allowed by default.

<br>OrderedSets are useful when fast associate lookup is important and when index-based lookup is unnecessary.

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<br>Strictly speaking, there is no reason why null is not a valid entry. However, most comparators (including the default HashComparator) will fail and throw an exception if you attempt to add a null entry because they cast the entry to a class and then activate one of its methods. It is perfectly possible to hand-craft a comparator that will accept null as a valid key.

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<br>There are many different approaches that could be used to implementing an associative container. For example, most of the older libraries used a hashing scheme for positioning and retrieving items. This implementation uses a data structure called a red-black tree. A red-black tree is a binary search tree that uses an extra field in every node to store the node's color. Red-black trees constrain the way that nodes may be colored in such a way that the tree remains reasonably balanced. This property is important for ensuring a good overall performance - red-black trees guarantee that the worst case performance for the most common dynamic set operations is O( log N ). One conseqence of using a binary tree for storage of data is that the items remain in a sorted order. This allows JGL users to iterate through an associative container and access its elements in a sequenced manner.

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<br>Insertion does not affect iterators or references.

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<br>Removal only invalidates the iterators and references to the removed elements.

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The Microsoft guidelines say that you 'could' use a parameterless method instead of a property to indicate to the caller that the result has to be calculated, and the caller might therefore consider cacheing it.

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<br>The trouble is, this is a statement about the implementation that is manifested in the published interface to the class. If you later decide to store the first and last items inside the class, you would then wish you had used a property in the first place.

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<br>In my opinion, rather than considering implementation and performance (which can be changed), it is better to think about whether the result is conceptually a property of the class, or conceptually a calculated result, as the caller would see it.

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<br>I think in this situation, they are calculated results and therefore should be methods: GetFirst and GetLast.