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Postings from June 2016
On Wed, Jun 01, 2016 at 10:56:42PM -0600, Karl Williamson wrote:
> This came up on another thread, but I think it should get its own airing.
>
> qr/ ^ {1,3} /x, warns with "Quantifier unexpected on zero-length expression"
>
> qr/ ^ * /x warns instead with "^ * matches null string many times", and
> generates code that will run a very long time.
>
> qr/ ^ ? /x doesn't warn. Nor does qr/ ^ {0,1} /x. But qr/ ^ {0,2} /x
> does warn.
>
> It is nonsensical to use a quantifier on an assertion, and for Perl to
> try to do so is not likely at all to be DWIM. So I believe we should
> deprecate these.
I'd say it's about as nonsensical as multiplying 0 with something,
or doing C< "" x 5 >, but we aren't deprecating those either.
I grant you, there are many examples where it doesn't make sense,
but it makes generating patterns easier if "$SUB_PATTERN$QUANTIFIER"
is always valid, regardless whether $SUB_PATTERN is a zero-length
expression.
Just as generated code doesn't have to care whether something on
the LHS of a multiplication is 0.
Abigail
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