in reply to Re: use/require $MODULE (a variable)
in thread use/require $MODULE (a variable)

Thanks all for your input. I have the require working OK now, although I have two questions:

1). The two forms of require are: 

     require MODULE;
     require "MODULE.pm";

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The first form (according to the book) translates '::' to '/' (on Unix systems), and also treats indirect object notation as methods, whereas the second form requires the '/' path separator and treats indirect object notation as basic function calls. So I really want the first form, so I need to call this with 
     eval "require $module";

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Is this right?

2). I realize though that I need to perform some trickery with the symbol tables, I think. What I want is my module PmLoader.pm to take it's LIST input, and then find and load each of THOSE modules into the main package. As I have it now, it's loading these into the PmLoader package, but not into main. So, as was pointed out, when I say 

     use Pmloader qw( ...args ...);

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it's the same as saying 
     BEGIN {
          require PmLoader;
          PmLoader->import( qw( ...args...));
     }

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But then in PmLoader's import method, if I only call 
     eval "require $module";

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I'm missing the import. But the import needs to be done to main, not to package PmLoader. Can anyone give me a hint how to proceed here?
From the scriptorium annex,
-cadphile

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Re: Re: use/require $MODULE (a variable)
by lestrrat (Deacon) on Mar 17, 2002 at 04:58 UTC

    Look into Exporter's export_to_level function. Somehting like this:

      # in your PmLoader module... 
  sub import 
  {
     ## do whatever you need to do, and then
     eval "
       require $module;
       $module->export_to_level(2);
     ";
     ## obivously, don't forget to check for errors
  }

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    Update: On a second thought, not all modules have a export_to_level function, so it's really better to separate out those two statements into two eval() calls... 

       eval "require $module";
   ## check for errors...
   eval "$module->export_to_level(2)";
   ## this one can/may fail, so may be just warn?
   ## or I guess you could check by doing
   ##
   ##   $module->can( 'export_to_level' );
   ##

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      lestrrat -- Thanks very much! The export_to_level(2) works! for modules that are inheriting Exporter.pm. We still have however, many old .pl libraries, some of which are packages, others which are just files of subroutines. Pretty much in all cases, those that are actually packages, don't require Exporter; and the .pl subroutine files certainly don't.

      Now in normal mode, the symbols for the subroutines in the subroutine libfiles would remain in main, since no package name caused Perl to change namespaces. But in my PmLoader, without an export functionality, these remain in PmLoader.

      So in both of these cases, I guess I should concoct a local export subroutine (based on the relevant code in Exporter.pm) to call, since export_to_level() can't be used. Or maybe I should play with package name switching... Again, thanks alot for your help!

      -cadphile.

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        Ah, I see, well, there are a few tricks you can do for plain .pl files... you could do (sort of) what Exporter is doing, which is symbol table munging, or you could cheat a little and do something like

           ## beware! very much untested, it's incomplete,      
   ## and it needs lots of error checking.
   use IO::File;

   sub import
   {
      ## if the module is a plain .pl file...
      my $fh = IO::File->new( $module );
      local $/ = undef;
      my $text = <$fh>;
      undef $fh;

      my $caller_pkg = ((caller())[0]
      eval "package $caller_pkg; $text";
   }

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        Obviously, this is a hack and it won't always work (furthermore, it's ugly). But at least you could *attempt* to load them files to the correct namespace. ;)

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Re: Re: use/require $MODULE (a variable)
by cadphile (Beadle) on Mar 17, 2002 at 04:47 UTC
    Just to restate what I just posted, I'm able to get through the eval "require $module"; without trouble, and @INC, and %INC are being appropriately updated.

    But!, if one of the loaded Modules uses Exporter to export its symbols into the caller package, the problem is that the caller package is not main! I.e. the Modules are not exporting their symbols into main. Hence, if I have a module that exports a subroutine symbol into main, if I 

       use Module;

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    directly, I can call the subroutine without a qualified package designator. But when my loader loads the Module, I can only call the subroutine with the fully qualified package name.

    Why isn't the Exporter working in this case to export the Module's symbols into main?

    thanks,
    -cadphile

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