[cesarb]

> It would be nice to have separate types for arrays and maps though. I don't understand why they were combined to begin with. Simplicity? Seems like there are more edge cases and gotchas the way things are now.

Combining arrays and maps in one type was the cause for a remotely exploitable vulnerability in Drupal this year, https://www.drupal.org/SA-CORE-2014-005.

I commented on that at https://lwn.net/Articles/618530/. Quoting from that comment:

"[...] most uses will treat it either as an array (list of items) or as a key/value store (map from key to value, or sometimes set of values), but rarely as both at the same time. [...] In this vulnerability, the programmer expected a sequence, and was handed a mapping. [...] all uses of a single variable should be consistent (never use a sequence method on a mapping variable or a mapping method on a sequence variable). As shown in this vulnerability, "foreach ($data as $i => $value)" is a mapping method; it should never be used on a sequence, even if it works."