12.8 Importing with Exporter

Earlier we skipped over that "and now magic happens" part where the import routine (defined by the module author) is supposed to take File::Basename::fileparse and somehow alias it into the caller's package so it's callable as fileparse.

Perl provides a lot of introspection capabilities. Specifically, you can look at the symbol table (where all subroutines and most variables are named), see what is defined, and alter those definitions. You saw a bit of that back in the AUTOLOAD mechanism earlier. In fact, as the author of File::Basename, if you simply want to force filename, basename, and fileparse from the current package into the main package, you can write import like this:

sub import {
  no strict 'refs';
  for (qw(filename basename fileparse)) {
    *{"main::$_"} = \&$_;
  }
}

Boy, is that cryptic! And limited. What if you didn't want fileparse? What if you invoked use in a package other than main?

Thankfully, there's a standard import that's available in the Exporter module. As the module author, all you do is add:

use Exporter;
our @ISA = qw(Exporter);

Now the import call to the package will inherit upward to the Exporter class, providing an import routine that knows how to take a list of subroutines^[12] and export them to the caller's package.

^[12] And variables, although far less common, and arguably the wrong thing to do.