Re^3: regex, find words that occur more than once.

[LanX]

I doubt that's autovivification.

x++ means x+=1 means x=x+1

I expect this to work in many languages, where undef+1 yields 1

[Fletch]

It's not; autovivification is defined in perlref and is perl automatically treating undef in an lvalue reference context as evaluating to a reference to a newly created item of the correct type (arrayref or hashref). This is at best just undefined in a numeric context (in this case coming from an empty slot in a hash) being treated as a numeric value of zero.

(Now were it $words{$something}->{$_}++ and $words{$something} wasn't defined for a given value of $something then it WOULD be an instance of autovivification (in which case a new hashref would be conjured up, stuck into $words{$something}, and then the key $_ in that new hashref would be looked up (and since it's an empty hash would evaluate to undef which would numerically be zero then that would be incremented to one, and finally that one stored back into that hashref)))

(But as usual for the source . . . INEW)

Edit: tweaked first paragraph to be even more technically correct (the best kind).