As I mentioned in a previous post, I would like to be able to view the lvaluable function referred to by a reference instead of just the result of said function.

Say what?

Take this simple example: my $lvalue = \substr("abc", 1, 1); If you print the dereference (print $$lvalue,"\n";), you see the result 'b' and not the function that was called. I want to see 'substr("abc", 1, 1);'.

I originally thought that this would be extremely hard to accomplish but I started fiddling around with the B module and I eventually stumbled upon a way that seems to work quite well for most lvaluable functions.

The only lvaluable function that is really causing me problems is keys. I cannot get the exact code back that is referenced but I can come close. You see if someone were to reference keys %imahash = 5;, my code would spit out keys %hash = 7; because 1) I cannot resolve the hash name and 2) it shows the actual space allotted instead of what was asked for. #2 is not an issue in my book, in fact I see this as being better. #1 is the hard part and why I'm posting. Is this possible? What should I read?

Here is my example script. Please note that there may be many mistakes because I'm doing this via trial and error. I have not found the right set of documentation yet.

#!/usr/bin/perl -w
use strict;
use B;

my $foo = ' delicious';
my $string = 'abcde';
my %imahash = (
  key => 3,
  foo => $foo,
  string => $string,
);

print "Testing vec:\n";
ltype(\(vec($foo,  0, 32) = 0x5065726C));

print "Testing keys:\n";
ltype(\(keys %imahash = 5));

print "Testing pos:\n";
ltype(\(pos $string = 3));


print "Testing pos:\n";
ltype(\(pos $string = 5));

print "Testing substr EXPR, OFFSET:\n";
ltype(\substr($string, 2));

print "Testing substr EXPR, OFFSET, LENGTH:\n";
ltype(\substr($string, 1, 2));

print "Done.\n";

sub enter {
  #print "Press any key to continue...\n";   # Original post
  print "Press Enter to continue...\n";      # Update
  $_=<STDIN>;
}

sub lvalue {
  my $ref = shift;
  my $lref = B::svref_2object($ref);
  return undef if $lref !~ /PVLV/;
  my $value = $$ref;
  my $type = $lref->TYPE;
  my $targ = $lref->TARG;
  my $string = $lref->TARG->PV;
  my $offset = $lref->TARGOFF;
  my $length = $lref->TARGLEN;
  print 'TYPE: ', $type,"\n";
  my $func;
  if ($type eq 'x') {
    $func = 'substr("'.$string.'",'.$offset.','.$length.');';
  }
  if ($type eq '.') {
    print "magic type: ", $targ->MAGIC->TYPE,"\n"; # 'g'
    $func = 'pos "'.$string.'" = '.$value.';';
  }
  if ($type eq 'k') {
    $func = 'keys %hash = ' . $targ->MAX . ';';
    
=comment
    print $targ->FILL,"\n";
    print $targ->MAX,"\n";
    print $targ->KEYS,"\n";
    print $targ->NAME,"\n";
    print $targ->RITER,"\n";
    print $targ->PMROOT,"\n";
=cut
    
    my %newhash = $targ->ARRAY;
    print "key\tvalue\t\t\tclass\ttrue value\n";
    foreach my $key (keys %newhash) {
      my $class = B::class($newhash{$key});
      print "$key\t$newhash{$key}\t$class\t",$newhash{$key}->$class,"\
+n";
    }
  }
  if ($type eq 'v') {
    $func = "vec('$string',$offset,$length) = $value;";
  }
  return $func;
}

sub ltype {
  my $lvalue = shift;
  print '$$lvalue: ',$$lvalue,"\n";
  print lvalue($lvalue),"\n";
  enter();
}

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Update at author's req. - dvergin 2003-05-29

In reply to Discovering the lvaluable function behind the reference by Mr. Muskrat

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