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How do I interpolate the value in a string variable into a constant in Perl?

April 27, 2022

I am writing a function in Perl, where a string is passed as an argument, and I need to interpret the string into the referenced value. The string would look something like this:
"Edible => 1;Fruit => STRAWBERRY;"
Now, the variable part will be stored using hashes, however, the value is already defined using constants. My question is, once I store the value into a temporary variable, how do I convert it into the value of the constant?
Here is some example code:

#!/usr/bin/perl

require Exporter;

our @ISA = 'Exporter';
our @EXPORT = qw(STRAWBERRY TANGERINE PEAR APPLE PERSIMMON FUNC_Interpreter);

use constant {
    STRAWBERRY => 1
   ,TANGERINE => 2
   ,PEAR => 3
   ,APPLE => 4
   ,PERSIMMON => 5
};

sub FUNC_Interpreter {
    my ($analyze_this) = @_;
    my @values;
    foreach my $str (split (/;/, $analyze_this)) {
        my ($key, $value) = split /=>/, $str;
        push (@values, @{[ $value ]});           # Problem line! I want to store the numeric value here. This doesn't work... :(
    }
}

FUNC_Interpreter ("HELLO=>TANGERINE;HELLO=>STRAWBERRY");

So basically, what I want to do is convert a string, which is actually the name of a constant stored in a variable, into a constant’s value. Is this possible?

>Solution :

Constants can be treated as subs.

{
   no strict qw( refs );
   push @values, $value->();
}

push @values, ( \&$value )->();

But that’s a hackish risky approach. And the second version even hides that you are dangerously allowing the user to call any sub in any package. What I would do instead:

my %lookup;
BEGIN {
   %lookup = (
      STRAWBERRY => 1,
      TANGERINE  => 2,
      PEAR       => 3,
      APPLE      => 4,
      PERSIMMON  => 5,
   );
}

use constant \%lookup;