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deprecating non-default postderef_qq

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Ricardo Signes
May 23, 2021 16:24
deprecating non-default postderef_qq
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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->@*"'

~$ 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.

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