>ContiguousArray</code>, and <code>ArraySlice</code> share an exponential growth
strategy that makes <code>append</code> a constant time operation <em>when
amortized over many invocations</em>.  In addition to a <code>count</code>
property, these array types have a <code>capacity</code> that reflects their
potential to store elements without reallocation, and when you
know how many elements you&#39;ll store, you can call
<code>reserveCapacity</code> to pre-emptively reallocate and prevent
intermediate reall