In perl, the string "aa" can be auto-incremented to become "ab" when various specific conditions are met. PHP has similar behavior, and references Perl, which I take to mean that the earlier use is with Perl.
Why was the magic behavior added to Perl in the first place?
An example discussion is here: Increment (++) and decrement (--) strings in Perl which notes that the perl docs do not give a rationale.
And that's my question: What was the original rationale behind creating the string auto-increment "magic" behavior?
2ND EDIT: This has nothing to do with autovivification. In researching possible answers to my rationale question, I misinterpreted what I was reading. Thanks ThisSuitIsBlackNot for pointing that out, and choroba for asking what I meant.
I completely agree that the feature IS useful, and I do use it whenever I make a reasonable excuse to do so, primarily as a generator of unique non-numeric tags/keys. I'm still wondering if there WAS a specific rationale or use case it was originally aimed at. We may never know!
Why was the magic behavior added to Perl in the first place?
Because it is useful. At the very least, it can be used to create non-numeric unique ids.
The most likely explanation that I can find is to support autovivication.
There's no relation between it and autovivification or references in general.
That is, it's relatively common to auto-increment a generated hash key.
Sure, if string ++ is used create unique ids, you might use a hash to lookup by id.