Re: Undefined subroutine errors

Design issues asside, Exporter needs to be loaded (and its configuration variables must be initialized) before the other module of the pair is loaded. Using the following templates will allow both modules to import from each other:

use strict;
use warnings;

package SpiderMan;

BEGIN {
   our @ISA = qw( Exporter ... );
   our @EXPORT_OK = qw( ... );
   require Exporter;
}

use ...;
use ...;
use Doctor::Octopus;
use ...;
use ...;

...

1;
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use strict;
use warnings;

package Doctor::Octopus;

BEGIN {
   our @ISA = qw( Exporter ... );
   our @EXPORT_OK = qw( ... );
   require Exporter;
}

use ...;
use ...;
use SpiderMan;
use ...;
use ...;

...

1;
[download]

Comment on Re: Undefined subroutine errors Select or Download Code

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Re^2: Undefined subroutine errors by Anonymous Monk on Oct 26, 2005 at 19:50 UTC
You were correct. It works now. Thanks. Can you or someone else please tell me why I need the BEGIN blocks?	[reply]
Re^3: Undefined subroutine errors by ikegami (Patriarch) on Oct 27, 2005 at 15:08 UTC
`use` and `BEGIN` are executed as soon as they are compiled. Without the `BEGIN`, the following would happen: Spiderman's `use strict;` is compiled. Spiderman's `use strict;` is executed. Spiderman's `use warnings;` is compiled. Spiderman's `use warnings;` is executed. What was in Spiderman's `BEGIN` is compiled. Spiderman's `use Doctor::Octopus;` is compiled. Spiderman's `use Doctor::Octopus;` is executed. `require Doctor::Octopus` is executed. Octopus's `use strict;` is compiled. Octopus's `use strict;` is executed. Octopus's `use warnings;` is compiled. Octopus's `use warnings;` is executed. What was in Octopus's `BEGIN` is compiled. Octopus's `use Spiderman;` is compiled. Octopus's `use Spiderman;` is executed. Spiderman is already loaded, so it's not loaded again. Spiderman is already loaded, so it's not executed again. `Spiderman->import` doesn't exist, so it isn't called. This is the problem. Exporter hasn't been loaded yet, and the variables telling Exporter what Spiderman should export haven't been initialized. The rest of Octopus is compiled. What was in Octopus's `BEGIN` is executed. The rest of Octopus is executed. The rest of Spiderman is compiled. What was in Spiderman's `BEGIN` is executed. The rest of Spiderman is executed. `Doctor::Octopus->import` is called. Remember that `use Module` [download] means `BEGIN { require Module; Module->import if Module->can('import'); }` [download]	[reply] [d/l] [select]