Hi all,

I have a bunch of applications using the following construct to import variables and their names into their namespaces: 

package Somepackage;

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

our @EXPORT_OK = qw($SOME_VAR);

our $SOME_VAR = 123;

1;

use Somepackage qw($SOME_VAR);

print "It is: $SOME_VAR\n";

[download]

Now I want to generate the Somepackage class dynamically as the variables and their values will be stored in a database table from now on.

That's all easy, just generate the appropriate code in a variable and eval the generated code using eval.

This boils down to the following example: 


##
## BEGIN makes available the variable $SOME_VAR, these declarations ar
+e
## read from a database in reality.
##

sub BEGIN
{
    my $varName  = 'SOME_VAR';
    my $varValue = 123;

    ##
    ## Dynamically create the package
    ##

    my $code = qq/
package Somepackage;

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

our \@EXPORT_OK = qw(\$$varName);

our \$$varName = $varValue;

1;
/;

    print $code, "\n";

    eval $code;

    ##
    ## Leaving out this line makes the "use Somepackage qw($SOME_VAR) 
+fail (Can't locate package
    ## Somepackage.pm in @INC ...).
    ##

    $INC{"Somepackage.pm"} = 'abc';
}


##
## Let's use it.
##

use Somepackage qw($SOME_VAR);

##
## And see if it's defined.
##

print "Var is $SOME_VAR\n";

[download]

The thing I somewhat worry about is that if I don't put the generated package in %INC, it doesn't work, it says: Can't locate package Somepackage.pm. If I put the package name into %INC, all is well.

However, what do I put as the value in %INC? Normally, these are filenames pointing back to the original source file. In this case, there is no physical file.

Putting some random value in it ('abc') works fine and I should be ok. Does perl ever use the actual value, expecting it to be a file and thus possibly causing havoc in my application?

Thanks, Bas.

In reply to Dynamic USE and %INC by Bas-i

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