hello, yes i'm still a beginner, and yesterday i come up with something never occured to me: the interpolation of a string was not done as expected (sub class of '0 type problem': you expect something wrong).

Why this is not working? 
#!perl
use strict;
use warnings;
$|++;
my ($comp,$first,@sec);

$comp = "descr is ".(defined $first ? q{$first} : 'null').' and list i
+s '.( @sec ? q{join ' ', @sec} : 'empty');
print "Oringinal:$comp\n";
&modify_first('UNO');
&modify_second (1);&modify_second (2);
&modify_first ('DUE');
&reset_second;


sub modify_first{$first = shift;    print "$comp\n";}
sub modify_second {push @sec, shift; print "$comp\n";}
sub reset_second {@sec=qw();        print "$comp\n";}

__OUTPUT__
Oringinal:descr is null and list is empty
descr is null and list is empty
descr is null and list is empty
descr is null and list is empty
descr is null and list is empty
descr is null and list is empty

[download]
I have found two approach at this problem: Re: Dreaming of Post Interpolation that propose an quoting-evaluating workaround (not suitable for thinks like  @sec ? @sec : 'empty') 
my $text = q{
  Dear $person,
  I know that this text is $adjective.
  But I wish it could be...

};

my $person    = 'Mom';
my $adjective = 'not interpolated';

print eval "qq{$text}";

__OUTPUT__

  Dear Mom,
  I know that this text is not interpolated.
  But I wish it could be...

[download]

Another monks come out with a sub solution:
my $n = sub {1};
my $m = sub {&$n*2};
my $o = sub {&$m*2};
my $s = sub {&$n." ".&$m." ".&$o."\n"};
print &$s;
$n = sub {2};
print &$s;

__OUTPUT__
1 2 4
2 4 8

[download]
The Perl faq propose:
  How can I expand variables in text strings?
    Let's assume that you have a string that contains placeholder vari
+ables.

        $text = 'this has a $foo in it and a $bar';

    You can use a substitution with a double evaluation. The first /e 
+turns
    $1 into $foo, and the second /e turns $foo into its value. You may
+ want
    to wrap this in an "eval": if you try to get the value of an undec
+lared
    variable while running under "use strict", you get a fatal error.

        eval { $text =~ s/(\$\w+)/$1/eeg };
        die if $@;

    It's probably better in the general case to treat those variables 
+as
    entries in some special hash. For example:

        %user_defs = (
            foo  => 23,
            bar  => 19,
        );
        $text =~ s/\$(\w+)/$user_defs{$1}/g;

[download]

And finally chromatic propose a real magic to create a red apple:
my $color = "red";
my $fruit = "apple";
my $name = "chromatic";

my $string = 'Hi, my name is $name.  Please hand me a $color $fruit.';
print ">>$string<<\n";    # demonstrate what we have

my $s2;
eval "\$s2 = qq/$string/";    # the real magic
print "->$s2<-\n";    # demonstrate the result

__OUTPUT__
>>Hi, my name is $name.  Please hand me a $color $fruit.<<
->Hi, my name is chromatic.  Please hand me a red apple.<-

[download]

OK. now i know. But there is something newer then years 2000 can I profit? A cleaner solution?

L*
there are no rules, there are no thumbs..

In reply to Interpolation: when it occurs? another beginner question.. by Discipulus

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