Object Oriented Callback

zaebst has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I've always had a problem with getting my modules to pass their subroutines as callbacks. Does anyone know the correct structure?

package WebUtil;

sub Gen_HTML
{ 
  my $self = shift; 
  
  # 
  # Do stuff to make html 

  $self->{$HTML} .= qq( html content stuff ); 

  return($self->{$HTML}); 
} 


sub run_pjx 
{ 
  my $self= shift; 
  my $pjx = new CGI::Ajax( 'exported_func' => sub
                                                 { 
                                                      my $in = shift; 
                                                      return("Changed 
+Main $in\n"); 
                                                 }, 

                              'skip_header'   => 1  
                         );  
  my $ref_Gen_HTML = sub { $self->Gen_HTML() }; 
  print $pjx->build_html( $self->{$WU_CGI} , &$ref_Gen_HTML ); 
  #note should be:   build_html( $cgi_object, \&callback_Function );  

}
[download]

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Re: Object Oriented Callback by ikegami (Patriarch) on Dec 17, 2008 at 05:31 UTC
`&$ref_Gen_HTML` is a (special form of) subroutine call. You want to pass the reference, `$ref_Gen_HTML`. `my $ref_Gen_HTML = sub { $self->Gen_HTML() }; print $pjx->build_html( $self->{$WU_CGI}, $ref_Gen_HTML );` [download] or just `print $pjx->build_html( $self->{$WU_CGI}, sub { $self->Gen_HTML() } );` [download] Please use `<c>...</c>` instead of `<pre>...</pre>` on PerlMonks.	[reply] [d/l] [select]
Re: Object Oriented Callback by kennethk (Abbot) on Dec 17, 2008 at 05:52 UTC
In addition to ikegami's wonderful advice, you should also be including `use strict;` and `use warnings;` to catch simple headaches. There's some reference material you may find valuable in perlref on callbacks (search term coderef). To store a code reference in a hash and call it, you can do the following: `my %hash = (code => sub{print 'x'}); &{$hash{code}};` [download]	[reply] [d/l] [select]
Re^2: Object Oriented Callback by zaebst (Initiate) on Dec 17, 2008 at 06:19 UTC
Thanks guys. After fixing the subroutine call, I found one more problem and got things working. I switched pre tags to c tags as well.	[reply]