<p>There shouldn't be too much duplication in the second option. We would say that the left child would have type <code>VantagePointTree<BallBound></code> and the right child would have type <code>VantagePointTree<HollowBallBound></code>, then we could just specialize <code>TreeTraits</code> for each of those classes with different values for the left and right children. But, the real difficulty there, which I did not think about earlier, is that what is returned when I call <code>Child(i)</code> is unclear, and there is no way to preserve the type fully. I can think of some ways, maybe, but it would be a bit backhanded.</p>
<p>The checks for <code>FirstPointIsCentroid</code> are actually used pretty often; at least once in every <code>Score()</code> call. So it is of some importance that those remain static compile-time constants. If we were to make those supported as runtime checks in some cases, we would need to</p>
<ul>
<li>change the boolean constants to constexpr functions that take TreeTypes as a parameter</li>
<li>for VP-trees, the function can't be constexpr, but instead looks at whether the TreeType parameter is true or false</li>
</ul>
<p>We already have the fourth option implemented, so it is easy to test. :)</p>
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