Consider Adding Implementations for Sets of Points

[Chris3606]

It would make sense for the primitives library to offer some sort of SparseSet implementation that works, at minimum, with Point, in some capacity.

Consider the use case of storing a subset of Point objects which reside on a grid view (a fairly common when dealing with grid and/or grid algorithms).

There are two options, currently, that don't involve creating custom data structures. The first, is to use an IGridView<bool> (probably BitArrayView, in most cases). This is quite memory efficient (around 1 bit per location on a grid), and provides very quick Contains operations. What it does not provide, is O(n) iteration over elements in the set; you instead have to iterate over all elements in the grid view; an operation proportional to the size of the grid, rather than the number of elements in the set.

In the case where you need iteration, you can instead use a HashSet<Point>. This provides O(1) contains, and O(n) iteration; but is not particularly CPU cache efficient, and involves allocating during Add and Remove operations; therefore this does not fit all use cases either.

In cases like this, where a grid size is known, and doing allocation up front is preferable to allocation during Add/Remove operations, a sparse set structure (good example here) can be useful. It provides O(1) contains, O(1) add and remove, and O(n) iteration with good cache locality, in exchange for a fixed max size (not a problem for grid views) and performing allocation up front (a trade-off that grid views make anyway).

Another option is something like BitArrayView paired with List<int>. This would provide some memory reduction over the set above, and still provide O(1) contains, O(1) add, and O(n) iteration, in exchange for O(n)` remove. This in particular may fit use cases that clear the set entirely, rather than removing items.