如何在Perl中的另一个模块子内部调用一个模块子

Question

I have created Perl modules under /my_project/ABC/ . The ABC folder contains three subroutine modules: Build.pm , Config.pm , and Operation.pm . There is a common subroutine in Operation.pm that I need to access from Config.pm , but when I tried i throws

"configureTheRepository" is not exported by the ABC::Config module`.

Here is the call stack.

Operation.pm

    package ABC::Operation;

    use strict;
    use warnings;

    use Term::ANSIColor qw(:constants);
    use File::Basename qw(dirname);
    use Exporter qw(import);
    use Term::ANSIColor qw( colored );
    use Data::Dumper qw(Dumper);
    use JSON::PP;
    use File::Basename qw(dirname);
    use Cwd  qw(abs_path);
    use ABC::Config qw(configureTheRepository);

    our @EXPORT = qw(commonFunc)

   sub commonFunc{
      #handle logic
    }
1;

Config.pm

    package ABC::Config;

    use strict;
    use warnings;

    use Term::ANSIColor qw(:constants);
    use File::Basename qw(dirname);
    use Exporter qw(import);
    use Cwd  qw(abs_path);
    use Cwd  qw(abs_path);
    use ABC::Operation qw(commonFunc); #Compilation failed when i insert this line.if i removed this my script will execute and but in runtime throws undefined commonFunc.

   our @EXPORT = qw(configureTheRepository);

   sub configureTheRepository{
      #handle logic
    }

1;

Please let me know where I made the mistake.

Answer 1

There is a circular dependency. use statements get done at compile time . That means before any actual code is run. So when you start your program, and the first thing it does is go into ABC::Operation , the following will happen:

• scan ABC::Operation for use statements
• load Term::ANSIColor
  • parsing switches to Term::ANSIColor
  • scan Term::ANSIColor for use statements ...
• parsing switches back to ABC::Operation
• load File::Basename
  • parsing switches to File::Basename
  • scan File::Basename
• parsing switches back to ABC::Operation
• ... a couple more of those
• load ABC::Config
  • parsing switches to ABC::Config
  • scan ABC::Config for use statements ...
• parsing witches back to ABC::Operation
  • import stuff from Term::ANSIColor, File::Basename, Exporter and Cwd; these do not get loaded again because Perl already loaded them before. It only imports the symbols into the current ABC::Config namespace
  • import the function commonFunc from ABC::Config; again, this has also already been loaded, so it doesn't load it again
  • throw an error because at this point, ABC::Config has not finished parsing, and it does not yet export a commonFunc symbol

This is a bit confusing, but it's a sign that your architecture is broken. If things are common, they can sure be in a common package. But that common package cannot use anything that uses it. If that's the case, whatever is using it also becomes common by definition.

The solution is to rethink which functions go where. Find the smallest possible parts, and put them in one package. That's the things every other package shares. Then use it where it's needed. The next things that use this shouldn't bring each other in. Only the last level should combine all of them. The dependency tree is called tree for a reason. Having a circle in there can't work.