Allow access to outer $_'s

[p5pRT]

Migrated from rt.perl.org#134466 (status was 'open')

Searchable as RT134466$

[p5pRT]

From @jidanni

Created by [email protected]

$ man perlvar

$_ : the default iterator variable in a "foreach" loop if no other
variable is supplied.

OK, but wouldn't it be neat if one could reference "outer $_'s" too,
without the fuss of naming them?

for ( $doc->createElement('Folder') ) {
  for ( $doc->createElement('Placemark') ) {
$__->appendChild($_);
for ( $doc->createElement('Camera') ) {
  $__->appendChild($_);
}
  }

Here $__ refers to the "parent $_".

A $___ could refer to the "grandparent $_".

Anyway, all of them are remembered in some stack, just currently not
accessible from inner loops, for "no good reason." ($__ probably isn't
the best name for it, I just made it up on the spur of the moment.
Maybe have a number in the variable indication how many levels up it
is to access.)

Perl Info

Flags:
    category=core
    severity=wishlist

Site configuration information for perl 5.28.1:...

[p5pRT]

From @jkeenan

On Wed, 02 Oct 2019 19​:45​:48 GMT, jidanni wrote​:

This is a bug report for perl from jidanni@​gmail.com,
generated with the help of perlbug 1.41 running under perl 5.28.1.

-----------------------------------------------------------------
[Please describe your issue here]

$ man perlvar

$_ : the default iterator variable in a "foreach" loop if no other
variable is supplied.

OK, but wouldn't it be neat if one could reference "outer $_'s" too,
without the fuss of naming them?

for ( $doc->createElement('Folder') ) {
for ( $doc->createElement('Placemark') ) {
$__->appendChild($_);
for ( $doc->createElement('Camera') ) {
$__->appendChild($_);
}
}

Here $__ refers to the "parent $_".

A $___ could refer to the "grandparent $_".

Anyway, all of them are remembered in some stack, just currently not
accessible from inner loops, for "no good reason." ($__ probably isn't
the best name for it, I just made it up on the spur of the moment.
Maybe have a number in the variable indication how many levels up it
is to access.)

I suspect that, given the many other uses of '$_' (perldoc perlvar), this would be an implementation nightmare and very bug-prone.

Thank you very much.

--
James E Keenan (jkeenan@​cpan.org)

[p5pRT]

The RT System itself - Status changed from 'new' to 'open'

[p5pRT]

From @tonycoz

On Wed, 02 Oct 2019 12​:45​:48 -0700, jidanni wrote​:

$ man perlvar

$_ : the default iterator variable in a "foreach" loop if no other
variable is supplied.

OK, but wouldn't it be neat if one could reference "outer $_'s" too,
without the fuss of naming them?

for ( $doc->createElement('Folder') ) {
for ( $doc->createElement('Placemark') ) {
$__->appendChild($_);
for ( $doc->createElement('Camera') ) {
$__->appendChild($_);
}
}

Here $__ refers to the "parent $_".

A $___ could refer to the "grandparent $_".

Anyway, all of them are remembered in some stack, just currently not
accessible from inner loops, for "no good reason." ($__ probably isn't
the best name for it, I just made it up on the spur of the moment.
Maybe have a number in the variable indication how many levels up it
is to access.)

They are remembered on the save stack, but it's non-trivial to get to it, which strikes me as not "no good reason".

We could make it simpler to get to those values (add magic to each $_ to point to the parent for example), but that would cost to all such localizing of $_, since $_ is global, and we don't know if the programmer is accessing $__, $___ etc in a called function.

The $__, $___ names are bad, since you'd forcing a maintainer to count _ which due to the _ glyph joining together will be difficult to count at a glance.

You could just name the values, which will make the code more readable.

Tony

[tonycoz]

I plan to reject this, unless someone else has an opposing opinion.

[jidanni]

OK go ahead. Maybe it wasn't a good idea.