sub {} inside of a foreach loop using $_ 1

[xhonzi]

So, I know this shouldn't be as hard as I'm making it,
but I've having trouble using $_ in a sub {} in a foreach loop.

@names=qw\Matt Todd Justin\;
foreach (@names) {
  $mw->Button(-title=>"$_",-command=>sub{print "My name is $_!\b"})->pack;
}

My $_ ends up being a "" when I push the button. I know there's a way to do this, and, in fact, I know I've done it before but for the life of me I can't figure it out.

xhonzi

 

[xhonzi]

I meant to also say that the title on the button shows up correctly. But I get "My name is !" from the print statement.

 

[MillerH]

Well, the most probable solution is don't use $_.

[url=http://perldoc.perl.org/functions/my.html][black][b]my[/b][/black][/url] [blue]@names[/blue] = [red]qw([/red][purple]Matt Todd Justin[/purple][red])[/red][red];[/red]
[olive][b]foreach[/b][/olive] [black][b]my[/b][/black] [blue]$name[/blue] [red]([/red][blue]@names[/blue][red])[/red] [red]{[/red]
	[blue]$mw[/blue]->[maroon]Button[/maroon][red]([/red]
		-[purple]title[/purple]   => [blue]$name[/blue],
		-[purple]command[/purple] => [url=http://perldoc.perl.org/functions/sub.html][black][b]sub[/b][/black][/url] [red]{[/red][url=http://perldoc.perl.org/functions/print.html][black][b]print[/b][/black][/url] [red]"[/red][purple]My name is [blue]$name[/blue]![purple][b]\b[/b][/purple][/purple][red]"[/red][red]}[/red],
	[red])[/red]->[maroon]pack[/maroon][red];[/red]
[red]}[/red]

Also, be sure to use strict in your code.

- Miller

 

[xhonzi]

But I love $_.

You can't 'my' in a foreach (@names) can you?

Frankly, your solution would work better, but I did, while writing this, think of adding a

 my $name=$_;[\code] in the loop so I could use $name and that worked. 

Thanks for the prompt reply.

xhonzi

 

[MillerH]

If you want to write maintainable code, then I strongly advise against the use of $_ except for the most rudimentary purposes such as in a map or grep clause. For any other time, you'll save yourself and others a lot of headache if you give your variables meaningful names.

Don't let laziness, and the desire to be cute, lead you into ineffectual coding practices.

And yes, you can include the my declaration for the iterator in a for or foreach.

If you insisted on using $_, this is how I would probably do it:

[url=http://perldoc.perl.org/functions/my.html][black][b]my[/b][/black][/url] [blue]@names[/blue] = [red]qw([/red][purple]Matt Todd Justin[/purple][red])[/red][red];[/red]
[olive][b]foreach[/b][/olive] [red]([/red][blue]@names[/blue][red])[/red] [red]{[/red]
    [blue]$mw[/blue]->[maroon]Button[/maroon][red]([/red]
        -[purple]title[/purple]   => [blue]$_[/blue],
        -[purple]command[/purple] => [url=http://perldoc.perl.org/functions/eval.html][black][b]eval[/b][/black][/url] [red]qq{[/red][purple]sub {print "My name is \Q$_\E!\b"}[/purple][red]}[/red],
    [red])[/red]->[maroon]pack[/maroon][red];[/red]
[red]}[/red]

- Miller

 

[Kirsle]

While MillerH's suggestion works, Tk actually has something to handle this kind of thing built in.

my @names = qw(Matt Todd Justin);
foreach (@names) {
   $mw->Button (
      -text => $_,
      -command => [
         sub {
            my $name = shift;
            print "My name is \Q$name\E\b";
         },
         $_,
       ],
   )->pack;
}

Basically, the -command attribute takes an array reference, where the first element is the subroutine, and the following elements are data to send to the subroutine. Sometimes $_[0] will be a reference to the widget itself though, so watch out for that (i.e. iirc Tk::Listbox's $_[0] is a reference to the listbox instead of the first bit of data you sent).

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