Hey Perl Monks,

I, a poor hacker, am confounded by the following problem. This isn't the problem I'm having (exactly), it's just the simplest case I can reduce it to.

Let's say you wanted to build a simple text file editor, using the following code:


use Tkx;
use strict;

our (@data, @editctls, @buttons);

open IN, "test.txt";
flock IN, 1;
@data = <IN>;
close IN;

chomp @data;


our $mw = Tkx::widget->new(".");

for (my $x = 0; $x < @data; $x++) {
    push @editctls, $mw->new_ttk__entry(-width => 30, -textvariable =>
+ \$data[$x]);
    $editctls[$x]->g_grid(-row => $x, -column => 0);
    
    push @buttons, $mw->new_ttk__button(-text => "Update", -command =>
+ sub { update($x); } );
    $buttons[$x]->g_grid(-row => $x, -column => 1);
}

Tkx::MainLoop();    


sub update {

    my $which = shift;

    open DATA, "+<test.txt";
    my @stuff = <DATA>;
    $stuff[$which] = $data[$which] . "\n";
    seek DATA, 0, 0;
    print DATA @stuff;
    truncate DATA, tell(DATA);
    close DATA;
}

[download]

And I'm using the following text file for testing:


this 
is
a
text
file

[download]

The problem is with the update buttons. When clicked, they send the current value of $x to the update subroutine, not the value of $x when the anonymous sub was created. I had thought that when anonymous subs refer to lexical variables, they created a closure, but apparently not so in this case. Am I missing something? Is there a correct way to do this?

I did try moving the control creation logic to an actual sub but it made no difference.

Thanks,

Lars Brandewie

In reply to Closure confusion in Tkx by lbrandewie

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