Study on hash associative arrays

[bearophile]

Through Reddit I've found posts about hash-based associative 
arrays:

http://bannalia.blogspot.it/2013/10/implementation-of-c-unordered.html
http://bannalia.blogspot.it/2014/01/a-better-hash-table.html

Those little images like this one are excellent at explaining in 
a short space the basic structure of a data structure:

http://4.bp.blogspot.com/-jh0W64vfSt8/UsmZMel5gQI/AAAAAAAAAvU/k6ThAu4mL2M/s400/boost.multiindex_1.png

I think the online documentation should have images like this one 
for AAs, and other data structures.

Do you know what's the structure of the D built-in AAs, and are 
the ideas in those two posts useful to improve D AAs?

Bye,
bearophile