Today’s article is inspired by Jean-Philippe Auclair’s excellent article on arrays and the comment he recently posted on my article about map performance. In it he discusses how the Array class is implemented using a densely-packed C/C++ array (a contiguous block of memory) and, after the first undefined element, a hash table. This got me thinking of three questions, together the subject of today’s article. First, when an Array‘s densely-packed portion is split using the delete operator, how fast is this? Secondly, can it be re-joined? Third, how fast is rejoining it?

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