Pd's data-structures don't have to be allocated as separate items. They can be allocated in array-fashion, as one big block.
What I say about Pd's data-structures doesn't apply to array-like types defined in other plugins, such as GridFlow, iemmatrix, iem16, Gem, PDP.
In theory, plugins can use data-structures and define new stuff about data-structures, but in practice, no-one ever did.
can you explain clearly what you meant in these 2 paragraphs?