executing subroutines via variable

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

I have a script that I would like to be able to have a seperate library of perl commands that would be called when a script executes a certain portion and a variable comes up.

Normally what I would do is

 if( $var1 eq "value X" )
  {
     #code
  }
[download]

What if you won't know the variable name so that if a variable ( like in a hash ) comes up it gets evaluated and thena sub containing the varname gets executed

if( $do_additional_test{ $var1 } eq "true" )
{
   &additional_test_module::$var1( object_vars{ $var1 ) );
)
[download]

Comment on executing subroutines via variable Select or Download Code

Replies are listed 'Best First'.
Re: executing subroutines via variable by Kanji (Parson) on Nov 19, 2002 at 17:16 UTC
Although it's tempting to use `eval` in a situation like this, I prefer (ab)using coderefs, either by employing a hash of anonymous subs (rather than subs proper)... `package atm; my %code = ( var1 => sub { print 1 }, var2 => sub { print 2 }, # ... varN => sub { print N }, ); package main; if ( exists $atm::code{$varN} ) { $atm::code{$varN}->( object_vars($var1) ); } else { # no matching sub }` [download] ... or testing for the existance of the sub you want to run with `can`, and executing the coderef it returns. `if ( my $sub = atm->can($varN) ) { $sub->( object_vars($varN) ); } else { # no matching sub }` [download] --k.	[reply] [d/l] [select]
Re: executing subroutines via variable by broquaint (Abbot) on Nov 19, 2002 at 17:27 UTC
This sounds like a good situation for a dispatch table e.g `my $dispatch = { foo => \&foo, bar => sub { print "an anon sub\n" }, baz => \&Package::function };` [download] Yes a dispatch table would be poifict. `<cough>` The hackish solution would be `my %dispatch = map { $_ => \&{$hash{$_}} } keys %hash;` [download] And definitely for the likes of obfu. Ahem. `</cough>` HTH `_________ broquaint`	[reply] [d/l] [select]
Re: executing subroutines via variable by dakkar (Hermit) on Nov 19, 2002 at 17:21 UTC
You can do that (see perlref): `('additional_test_module::'.$var1)->(object_vars($var1));` [download] But I think you don't want to. There are some problems with the approach: It doesn't work under 'strict' (and you are using strict, aren't you?) It can blow up in your face if the variable contains something strange (like, spaces...) It's ugly `;-)` A better approach is: `our %subs=('value X'=>\&module::subX, 'value Y'=>\&module::subY, 'somethingelse' => \&module::else); $var=get_the_var(); if (test($var)) { if (exists $subs{$var}) { $subs{$var}->(object_vars($var)) } else { signal_error($var) } }` [download] This stores all known subs in a hash, then calls the right one. Oh, I'm assuming that when you say "don't know the variable name" you mean the "value". If you really don't know the possible values of the var, or the possible subs to call, then you have other problems than to worry about 'strict', so you can go with my first code, and in the meantime re-design the system `;-)))` -- dakkar - Mobilis in mobile	[reply] [d/l] [select]