Modules use each other in cycle. Compilation error in Perl

Question

There are 3 modules, so that they use each other by pattern a -> b -> c -> a. I cannot compile such case.

For instance,

I get a compilation error

"Throw" is not exported by the LIB::Common::Utils module
Can't continue after import errors at /root/bin/ppm/LIB/Common/EnvConfigMgr.pm line 13
BEGIN failed--compilation aborted at /root/bin/ppm/LIB/Common/EnvConfigMgr.pm line 13.

Utils.pm

use Exporter qw(import);
our @EXPORT_OK = qw(
        GetDirCheckSum
        AreDirsEqual
        onError
        Throw);
use LIB::Common::Logger::Log;

Log.pm

use Log::Log4perl;

use LIB::Common::EnvConfigMgr qw/Expand/;

EnvConfigMgr.pm

use Exporter qw(import);

our @EXPORT = qw(TransformShellVars ExpandString InitSearchLocations);
our @EXPORT_OK = qw(Expand);

use LIB::Common::Utils qw/Throw/;

Why doesn't it get compiled and how to make it work?

Answer 1

You need to use require instead of use somewhere in the loop of dependencies so as to delay the binding. It is most convenient with a module that exports nothing, as otherwise you need to write an explicit import call

In your case LIB::Common::Logger::Log doesn't use Export, so putting

require LIB::Common::Logger::Log

into LIB/Common/Utils.pm fixes the problem

You have access to the code that isn't working, and you could have saved us a lot of time by simply showing the malfunctioning code. You ignored two comments asking for more information so I have set up these files

Note that this code does nothing: it simply compiles

LIB/Common/Utils.pm

package LIB::Common::Utils;

use Exporter 'import';

our @EXPORT_OK = qw/
    GetDirCheckSum
    AreDirsEqual
    onError
    Throw
/;

require LIB::Common::Logger::Log;

sub GetDirCheckSum { }

sub AreDirsEqual { }

sub onError { }

sub Throw { }

1;

LIB/Common/Logger/EnvConfigMgr.pm

package LIB::Common::EnvConfigMgr;

use Exporter 'import';

our @EXPORT = qw/ TransformShellVars ExpandString InitSearchLocations /;
our @EXPORT_OK = 'Expand';

use LIB::Common::Utils 'Throw';

sub TransformShellVars { }

sub ExpandString { }

sub InitSearchLocations { }

sub Expand { }

1;

LIB/Common/Logger/Log.pm

package LIB::Common::Logger::Log;

use Log::Log4perl;

use LIB::Common::EnvConfigMgr 'Expand';

1;

main.pl

use strict;
use warnings 'all';

use FindBin;
use lib $FindBin::Bin;

use LIB::Common::Utils;