Use of Constants

Adorn has asked for the wisdom of the Perl Monks concerning the following question:

Hi I am new to perl so please help me even though my question is idiotic to you

   
#! /usr/bin/perl 

use constant VARS => {X => 20, Y => 20};
use constant EQ => [2*Y, -2*X*Y];
$x = VARS -> {X};
$y = VARS -> {Y};
print "Val of \$x is $x \n";
print "Val of \$y is $y \n";

$temp = EQ ->[0];
print "$temp \n";

print EQ->[1]."\n";
[download]

I get warnings even without -w saying : operator or Semicolon missing Unambiguous use of *

So can't I use already defined constants in other constants. Here, as you might have run the code, EQ->[0] or EQ->1 is not evaluated.

Appreciate any help..

Comment on Use of Constants Download Code

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Re: Use of Constants by choroba (Cardinal) on Jul 24, 2012 at 13:50 UTC
You have not defined X and Y, you have defined `VARS->{X}` and `VARS->{Y}`.	[reply] [d/l] [select]
Re^2: Use of Constants by Adorn (Initiate) on Jul 24, 2012 at 19:04 UTC
Thanks for reply.. You have brought my attention to something stupid i was doing.. but i guess this is what i call learning a new language.. using separate use constants for each X and Y solves my problem and also use of VARS->X is correct. Thank You all.. I do not know if this forum has a rule of marking question as solved or something like that.. bit busy today... so have no time to read the rules.. In that case someone can please mark this problem as "SOLVED"	[reply]
Re^3: Use of Constants by AnomalousMonk (Archbishop) on Jul 24, 2012 at 19:14 UTC
In that case someone can please mark this problem as "SOLVED" You mark the problem as 'SOLVED' by going away satisfied with a solution.	[reply]
Re: Use of Constants by nemesdani (Friar) on Jul 24, 2012 at 13:47 UTC
Try to insert a space before the *-s :) I'm too lazy to be proud of being impatient.	[reply] [d/l]
Re^2: Use of Constants by Adorn (Initiate) on Jul 24, 2012 at 18:52 UTC
Thanks for reply.. inserting space does not make any difference in this case though..!	[reply]
Re^3: Use of Constants by Adorn (Initiate) on Jul 24, 2012 at 18:56 UTC
Except warnings are gone.. But the value is still zero..	[reply]
Re: Use of Constants by kcott (Archbishop) on Jul 25, 2012 at 01:40 UTC
You appear to have a solution to your immediate problem. As you're new to Perl, I'll draw your attention to constant - CAVEATS. Not knowing that in certain circumstances you need to prepend `+`, or append `()`, to your constant names can be a source of problems that can be hard to track down. Readonly was suggested above. While this module addresses the `use constant` issues, it also has its drawbacks: see the CONS section in its documentation. Another alternative is Const::Fast. This addresses both the `constant` and `Readonly` issues but has its own CAVEATS. -- Ken	[reply] [d/l] [select]
Re: Use of Constants by 2teez (Vicar) on Jul 24, 2012 at 20:48 UTC
Hi, Instead of use constant, why don't you try use Readonly like so: `#! /usr/bin/perl use Readonly; Readonly my $vars => { X => 20, Y => 20 }; Readonly my $eq => [ 2 * Y, -2 * X * Y ]; $x = $vars->{X}; $y = $vars->{Y}; print "Val of \$x is $x \n"; # print 20 print "Val of \$y is $y \n"; # print 20 $temp = $eq->[0]; print "$temp \n"; # print 0 print $eq->[1] . "\n"; print 0` [download] However, to get desired print out for both `print "$temp \n"; # and print $eq->[1] . "\n";` [download] You could could have: `Readonly my $eq => [ 2 * $vars->{Y}, -2 * $vars->{X} * $vars->{Y} ]; ### instead of Readonly my $eq => [ 2 * Y, -2 * X * Y ];` [download] Then you have: `print "$temp \n"; ## prints 40 # and print $eq->[1] . "\n"; ## prints -800` [download]	[reply] [d/l] [select]