I have to wonder if exists could be patched to not have this behavior. Short-circuiting comes to mind. If $h{1} doesn't exist, $h{1}{2} certainly won't. I'd look at it, but I can't code my way out of a paper bag in C. Plus, I have to believe that I'm not the first person to come up with such a notion.
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I have to wonder if exists could be patched to not have this behavior. Short-circuiting comes to mind.
It wouldn't be easy. By the time the exists op is called,
all but one of the derefs has already taken place. IE exists
is essentially a binary operator taking a hash and key as args:
exists $hash{a}{b}{c}
is executed as:
exists(%{$hash{a}{b}}, 'c')
Dave. | [reply]
[d/l]
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It shouldn't be particular to exists(), it should be a general rule: autovivification should only happen to lvalues. When non-lvalues are evaluated, they short-circuit as soon as they encounter an undefined component, and return undef. exists() naturally returns false when checking a component of an undef (e.g., your latter example evaluates as exists(undef, 'c')).
Of course, there's probably some code by now that relies on autovivification of non-lvalues, and that argues strongly against implementing this suggestion. I can't think of any other arguments against it, though doubtless someone else can.
We're not really tightening our belts, it just feels that way because we're getting fatter.
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[d/l] |