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Re: deprecating non-default postderef_qq

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Leon Timmermans
May 23, 2021 17:27
Re: deprecating non-default postderef_qq
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On Sun, May 23, 2021 at 6:24 PM Ricardo Signes <>

> Porters,
> I continue to work through my list of cruft, experiments, and old
> defaults.  Today:  *postderef_qq*.
> ~$ perl -le '$r=[1,2,3]; print "@$r"'
> 1 2 3
> ~$ perl -le '$r=[1,2,3]; print "$r->@*"'
> ARRAY(0x7fc04080a648)->@*
> ~$ perl -lE '$r=[1,2,3]; print "$r->@*"'
> 1 2 3
> In that last one, -E turns on the postderef_qq feature, which allows
> postfix dereferencing inside of interpolative strings.  This was made
> separate from postderef because it was less clearly invalid syntax.  After
> all, that second one-liner did run.  And if its $r had been an object with
> stringification, or just a string, it might have even made sense.
> That said, I believe this is a very niche feature that we are better
> served by eliminating.  To do this, I propose:
>    - In 5.36.0:  We make cases where postderef_qq would occur, if not for
>    the feature being off, issue a deprecation warning, but act as before.
>    That is:  "Eat more $pies->@{ $x }" will interpolate $pies and @$x but also
>    warn.  User can eliminate the warning by changing their code to read "Eat
>    more $pies\->@{ $x }".
>    - In 5.40.0:  We make postderef_qq effectively on by default, without
>    the option to disable it, as postderef itself is.
> This is not a massive improvement in the language, and I'm not here to
> sell it as one.  It's a small reduction in complexity by making the syntax
> just a bit more consistent.  This is a bit like our work to call out the
> use of not-really-there metacharacters like \j or left braces that
> parameterize nothing in regex.  I am specifically not attempting to provide
> a generalized "interpolate an expression" syntax here.

I agree with this. I have always thought that splitting this into two
features didn't make much sense (and in fact, use experimental always
enabled postderef_qq if you enabled postderef)


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