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

I'm wondering if there is a better (safer, faster, etc.) way of dynamically loading a class by it's name, and then invoking the constructor (using the class name). The key is we don't want to have to say "use BAREWORD_CLASS", but want to get some of the same benefits. Here's what I'm doing now:

sub creator_func
{
   my ($class, $arg1, $arg2) = @_;

   eval "require $class";
   if ($@)
   {
        print "Load error for class='$class': $@\n";
        return;
   }

   my $new_obj = $class->new ($arg1, $arg2);
   return $new_obj;
}

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Is this inefficient? Will it compile the perl class every time it hits the require statement?

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Re: Dynamic Class Loading, Compilation, & Speed
by zwon (Abbot) on Mar 06, 2010 at 22:56 UTC

    You can use Module::Load for loading module. It actually doing the same(not exactly the same) eval you do, but just looks nice. As for creating new object, I don't think it may be better. 

    use Module::Load;
sub creator {
    my $class = shift;
    load $class;
    $class->new(@_);
}

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Re: Dynamic Class Loading, Compilation, & Speed
by jdrago999 (Pilgrim) on Mar 07, 2010 at 02:21 UTC

    Try this: 

    #!/usr/bin/perl -w

use strict;
use warnings 'all';

# ...later...

load_class("Some::Class");

sub load_class {
  my ($class) = @_;
  
  (my $file = "$class.pm") =~ s/::/\//g;
  unless( $INC{$file} ) {
    require $file;
    $class->import;
  }# end unless();
}# end load_class()

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    Just as use <ClassName> operates in compile-time, require operates in runtime without a string eval.

    To finish the job, call import on the newly-loaded package and you're done.

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      Nitpick... to handle the equivalent of use Module qw(foo => 'bar'); - 

      
# ...later...

load_class("Some::Class", @load_args);

sub load_class {
  my $class = shift;
  
  (my $file = "$class.pm") =~ s|::|/|g;
  unless( $INC{$file} ) {
    require $file;
  }# end unless();
  $class->import(@_);
}# end load_class()

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Re: Dynamic Class Loading, Compilation, & Speed
by cdarke (Prior) on Mar 06, 2010 at 23:04 UTC
    Rather than using eval with a string, it is probably better to use a block. For example:
    y $class = 'gash';
eval {
    require "$class.plm"
};

die "Oops: $@" if $@;

my $obj = $class->new();

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    It will not recompile the class each time, perl maintains %INC to record modules loaded.
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      require "$class.plm"

      Note, that won't work if $class='My::Class', you have to replace '::' with '/'. Module::Load takes care about this.

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Re: Dynamic Class Loading, Compilation, & Speed
by Anonymous Monk on Mar 06, 2010 at 23:21 UTC
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