CODEWITHSUNDEEP
perlpackage
Frerich Raabe
Frerich Raabe

Reputation: 94349

How can I get the symbols in a package at the time the package is defined?

In a Perl program I'm working on, the user can specify a Perl module to be loaded which is expected to define a couple (a variable number) of variables. The Perl program then processes these variables, basically treating the package as a plain hash except that the values are all in a namespace. Doing so works fine, i.e. this program prints '2':

use strict;
use warnings;

package P {
    my $k1 = 'v1';
    my $k2 = 'v2';
};

my $n = scalar keys %P::;
print "Number of entries: $n\n";
# print $P::x;

However, uncommenting the last line makes the program print '3'. I.e. the sheer mentioning of a variable in the package seems to add it to the symbol table.

Is there a way to get the symbol table for a package as it is defined, such that the symbol table consists of just two entries?

Upvotes: 3

Views: 244

Answers (1)

mob
mob

Reputation: 118605

Package variables encountered at compile-time will be added to the stash at compile time. So your workarounds are to evaluate the stash in the compile phase

package P {
    $k1 = 'v1';
    $k2 = 'v2';
};

BEGIN {    
    my $n = scalar keys %P::;
    print "Number of entries: $n\n";  # 2
}
print $P::x;

or to define other package variables at run-time

package P {
    $k1 = 'v1';
    $k2 = 'v2';
};

my $n = scalar keys %P::;
print "Number of entries: $n\n";    # 2
print eval '$P::x';
$n = scalar keys %P::;
print "Number of entries: $n\n";    # now 3

Upvotes: 5

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