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in reply to Re^3: Perl's feature to determine, in current point of loop, that this is the last one?
in thread Perl's feature to determine, in current point of loop, that this is the last one?

WRT use case: one of the (admittedly few) places I've seen something like this (which is why I mentioned the iterator module from TT) is in templating where you want to "decorate" the first or last item in a list differently than other items. Think maybe pagination where displaying a chunk from the middle and you want those items to have a link to the next or subsequent sets of results (terrible handwavy sample follows, and yes you could do similar stuff with JS or CSS instead). 

<table>
[% FOREACH item IN current_chunk %]
<tr>
[% IF loop.first %]<td> &lt;&lt; </td>[% ELSE %]<td>&nbsp;</td>[% END 
+%]
<td>[% item %]</td>
[% IF loop.last%]<td> &gt;&gt; </td>[% ELSE %]<td>&nbsp;</td>[% END %]
</tr>
[% END %]
</table>

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Edit: And I realized I hadn't linked to the TT FOREACH docs which explain the loop magic (which is Template::Iterator under the hood).

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The cake is a lie.
The cake is a lie.

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Re^5: Perl's feature to determine, in current point of loop, that this is the last one?
by talexb (Chancellor) on Jan 25, 2022 at 21:24 UTC

    Yeah, that's doable. I can also think of doing it without having everything inside the loop .. 

    #!/usr/bin/perl

use strict;
use warnings;

#  2022-0125: Handle First and List iems differently that everything
#  in between ..

{
    my @keys = qw/q w e r t y u i o p/;

    print "First is $keys[0] ..\n";

    foreach my $k ( @keys[1..(scalar @keys -2)] ) {

      print "In the middle: $k\n";
    }

    print "Finally, we have $keys[-1].\n";
}

    [download]
    This produces the output 
    First is q ..
In the middle: w
In the middle: e
In the middle: r
In the middle: t
In the middle: y
In the middle: u
In the middle: i
In the middle: o
Finally, we have p.

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    But I like your solution of using an Iterator -- then it has the job of handling the 'first' and 'last' issues.

    Alex / talexb / Toronto

    Thanks PJ. We owe you so much. Groklaw -- RIP -- 2003 to 2013.

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      Edge case behaviour might need some changes:

      #!/usr/bin/perl

use strict;
use warnings;

#  2022-0125: Handle First and List iems differently that everything
#  in between ..

{
    # my @keys = qw/q w e r t y u i o p/;
    my @keys = qw/q/;

    print "First is $keys[0] ..\n";

    foreach my $k ( @keys[1..(scalar @keys -2)] ) {

      print "In the middle: $k\n";
    }

    print "Finally, we have $keys[-1].\n";
}

      [download]
      B:\>perl 11140865-single.pl
First is q ..
Finally, we have q.

B:\>

      [download]

      Alexander

      --
      Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)
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