in reply to Invoking a string reference to a anonymous subroutine

I prefer dispatch tables since they allow full control. Otherwise use eval to handle lexical symbolic references. The third solution shows a way to note it in one line. HTH! =) 
use warnings;
use strict;


my $_parse_element_configuration =
  sub{
    print "element_configuration: @_\n"
  };

my $handler = "_parse_element_configuration";

my $self=42;



#--- dispatch table

my %parser;
$parser{_parse_element_configuration}=$_parse_element_configuration;

my $meth=$parser{$handler};
$self->$meth(666);


#--- lex sym ref via eval

$meth= eval "\$$handler";
$self->$meth(777);


#--- abstracted

sub handle {
  my $name=shift;
  return eval "\$$name";
}

handle($handler)->($self,888);

[download]
out: 
element_configuration: 42 666
element_configuration: 42 777
element_configuration: 42 888

[download]

Cheers Rolf

( addicted to the Perl Programming Language)

update

corrected c&p problem but created duplicate! :-(

Replies are listed 'Best First'.
Re^2: Invoking a string reference to a anonymous subroutine
by AnomalousMonk (Archbishop) on Jan 14, 2014 at 22:43 UTC 
    #--- dispatch table
...
$self->$meth(666);
...
#--- lex sym ref via eval
...
$self->$meth(777);

    [download]

    Don't both of these approaches take the interpreter on a useless (if there is no '42' package/class) or potentially bugilicious (if there is such a package and it contains a  _whatever method) run time search through the  @ISA tree? Why use the  -> operator to pass an ordinary (i.e., non-class/object reference) parameter? Only
        #--- abstracted
        ...
        handle($handler)->($self,888);
    avoids this possibly lengthy detour, but substitutes eval work at runtime.

    Of course, I'm not sure how one would create a '42' package in the first place, but what if it had been  $self = 'Foo'; in your example?

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        I see: the trick is the RHS of the  -> must be a code reference. Hmmm... I dunno...

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Re^2: Invoking a string reference to a anonymous subroutine
by Superfox il Volpone (Sexton) on Jan 15, 2014 at 11:15 UTC
    Hi there,
    thanks for your replies.

    I have tried the third approach by Lanx, but the program returns the following error: 
    Variable "$_parse_element_configuration" is not available at (eval 8) 
+line 2.
Use of uninitialized value in subroutine entry at Configuration.pm lin
+e 64.

    [download]
    My code is : 
    my $_parse_element_configuration = sub{ ... }

sub _handler{
  my $function_name = shift;
  eval "\$$function_name";
};

[...]

# invoking the handler
_handler("_parse_element_configuration")->($self, $element);

    [download]
    Where is the problem?

    Kind regards,
    s.fox

    p.s. my Perl version is 5.10, could it be involved?
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      > Where is the problem?

      My code worked and the code you are showing now will also work.

      But maybe you should care to define _handler within the scope of your private $_parse... variables to have a proper closure?

      Otherwise Variable "$_parse_element_configuration" is not available at (eval 8) line 2."

      Cheers Rolf

      ( addicted to the Perl Programming Language)

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        Hi Rolf,

        thanks for your reply.

        But maybe you should care to define _handler within the scope of your private $_parse... variables to have a proper closure?
        I believe you are right. I have come up with the following code: 
        my $_parse_handler = sub {
  my $self = shift;
  my $function = shift . '0';
  
  # installed handlers
  my $_parse_element_configuration0 = $_parse_element_configuration;
  my $_parse_element_machines0 = $_parse_element_machines;
  
  eval "\$$function";
};

[...]

my $handler = $self->$_parse_handler("_parse_element_" . $element->nam
+e() );
$self->$handler($element);

        [download]
        Anyway I am getting the impression I am trying to bend the language to something it was not designed to do.

        Kind regards,
        s.fox
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[d/l]

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