Re: Perl "Constants"

You can also create a constant like this:

*SOME_CONSTANT = \ 'the value';
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Then these will be possible:

$h{$SOME_CONSTANT};

print "$SOME_CONSTANT\n";
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but

$SOME_CONSTANT = 'new value';
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would die with "Modification of a read-only value attempted at ... ".

This is documented in perlmod under "Symbol Tables".

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Re^2: Perl "Constants" by vessko (Initiate) on Feb 03, 2011 at 23:04 UTC
Small problem is that these are package variables (not 'my'-able). Under 'use strict' U have to 'our' them. In case U want the freedom to choose between package or lexical, I use this: use CONSTANT; CONSTANT my $E => 2.73, my $PI => 3.14, my $CREDO => 'The dream of the slave is...to become master +and have slaves'; # Oops! Wrong CREDO ;) $CREDO = 'In $$$ we trust!'; # will ERROR out ;) # and U can: print "I still believe that '$CREDO!'\n"; #where package CONSTANT; use Carp; use Exporter; use Tie::Scalar; @ISA = qw(Tie::StdScalar Exporter); @EXPORT = qw(CONSTANT); # sub CONSTANT {my $i=0;tie $_[$i++],__PACKAGE__,$_[$i++] while $i<@_} sub CONSTANT {tie $_[$.++],__PACKAGE__,$_[$.++] while $. < @_} # If you want to know if something is tied somewhere ;) # sub REF {@_ > 1 ? '' : ref tied $_[0] \|\| ref $_[0]} sub STORE {confess "constants are READ ONLY!"}; 1; vess [download]	[reply] [d/l]

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Re^2: Perl "Constants"
by vessko (Initiate) on Feb 03, 2011 at 23:04 UTC


use CONSTANT;

CONSTANT my $E     => 2.73,
         my $PI    => 3.14,
         my $CREDO =>   'The dream of the slave is...to become master 
+and have slaves';

# Oops! Wrong CREDO ;)
$CREDO = 'In $$$ we trust!'; # will ERROR out ;)

# and U can:
print "I still believe that '$CREDO!'\n";

#where

package CONSTANT;
use Carp;
use Exporter;
use Tie::Scalar;
@ISA = qw(Tie::StdScalar Exporter);
@EXPORT = qw(CONSTANT);

# sub CONSTANT {my $i=0;tie $_[$i++],__PACKAGE__,$_[$i++] while $i<@_}
sub CONSTANT {tie $_[$.++],__PACKAGE__,$_[$.++] while $. < @_}
# If you want to know if something is tied somewhere ;)
# sub REF {@_ > 1 ? '' : ref tied $_[0] || ref $_[0]}
sub STORE {confess "constants are READ ONLY!"};
1;

vess
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