Question

I want to make a small GUI using Tk in Perl that will have 2 buttons: Race and Quit.

I want the Race button to run a function that is located in a module Car and is called Race.

I’ve written the following code:

#!/usr/bin/perl -w

use strict;
use warnings;
use Car;
use Tk;

my $mw = MainWindow->new;
$mw->Label(-text => "The Amazing Race")->pack;
$mw->Button(
        -text    => 'Race',
        -command => sub {Car->Race()},
)->pack;
$mw->Button(
        -text    => 'Quit',
        -command => sub { exit },
)->pack;
MainLoop;

It works, but It seems stupid to me to make an unnamed subroutine that will just call another subroutine. But when I tried to use -command => sub Car->Race(), or -command => sub \&Car->Race(), it didn’t work.

I understand that this is because I’m not passing a reference to the function. How do I pass a reference to a function that is located in another namespace (module)?

Answer 1

This syntax is symple:

$mw->Button(
        -text    => 'Race',
        -command => \&Car::Race,
)->pack;

But if you need to pass any special arguments to that functions or call it as method, you still need an anon sub:

$mw->Button(
        -text    => 'Race',
        -command => sub { Car->Race(@_) },
)->pack;

This one calls Race as method of package Car and pass all arguments to it.