in reply to Re: Perl/Tk binding Tab
in thread Perl/Tk binding Tab

It works, thank you. Can you explain this. I am not sure I understand it: ($after{$_[0]} // $_[0])->focus;

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Re^3: Perl/Tk binding Tab
by Tux (Canon) on Oct 31, 2018 at 18:05 UTC

    // is the defined-or operator. If the left part is undefined, take the right part else take the left part.

    my $c = $a // $b;

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    Is like

    my $c = defined $a ? $a : $b;

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    but easier and chainable

    my $x = $a // function ($b) // $ENV{FOO} // $self->bar // 0;

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    Enjoy, Have FUN! H.Merijn
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Re^3: Perl/Tk binding Tab
by zentara (Cardinal) on Oct 31, 2018 at 18:16 UTC
    Hi, it may help to know that the calling widget is the first argument $_[0] pass to any Tk callback. This code may show you what is happening. Notice how the Entry widget changes with each Tab. 
    #!/usr/bin/perl

use strict;
use warnings;
use Tk;

my $mw = MainWindow->new();
my $entry1 = $mw->Entry()->pack();
my $entry2 = $mw->Entry()->pack();
my $entry3 = $mw->Entry()->pack();

my %after = ($entry1 => $entry2,
             $entry2 => $entry1,
          );

$mw -> bind('all','<Tab>',sub{ 
                  print "@_\n";
                ($after{$_[0]} // $_[0])->focus;
            }
            );

$mw->MainLoop();
exit(0);

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    I'm not really a human, but I play one on earth. ..... an animated JAPH
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