Re^4: Designing a DWIMish interface for generator function

Did you have a look at the code I linked to? It keeps the state, by using the ref of the iterator-variable as key:

 use strict;
use warnings;
 
{ my %lists;
 
  sub deal {
    my $aref=shift;
    my $id= \$_[0];
    #print $aref,$id;
    $lists{$id}=$aref if (! exists $lists{$id} );
    if (@{$lists{$id}}){
      for(@_) {
    $_=shift @{$lists{$id}};
      }
      return 1; 
    } else {
      delete $lists{$id};
      return 0;
    }
  }
}
 
$\="\n";
 
#--------- here we go 
while (deal [1..9] => my ($a,$b,$c) ){
  print $a,$b,$c;
  while (deal [a=>1,b=>2] => my ($a,$b) ){
    print $a,$b;
  }
}
#--------- 
print "EXIT";
 
__DATA__ 
123
a1
b2
456
a1
b2
789
a1
b2
[download]

But I have to admit that till now I haven't thought about last, that's indeed a problem...

Cheers Rolf

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Re^5: Designing a DWIMish interface for generator function by ikegami (Patriarch) on Feb 01, 2010 at 05:53 UTC
You assumed that the iterator variable will be created at the same memory address every pass of the loop. It's a bad assumption. For example, the following code is an infinite loop: `my @x; while (deal [1..9] => my ($a,$b,$c) ){ print $a,$b,$c; push @x, \$a; }` [download] Well, maybe not infinite, since `deal` is leaking memory every pass of the loop... You assumed that the loop will receive a new iterator each time. It's a bad assumption. For example, `deal` starts at the wrong number the second and third pass of the outer loop in the following code: `for (1..3) { while (deal [1..9] => my ($a,$b,$c) ){ print $a,$b,$c; last; } }` [download] Just like you need to call `keys` before `each`, you'd need to reset the iterator before entering the loop. You'd need `init_deal my ($a,$b,$c) while (deal [1..9] => ($a,$b,$c) ){ ... }` [download]	[reply] [d/l] [select]
Re^6: Designing a DWIMish interface for generator function by LanX (Saint) on Feb 01, 2010 at 11:12 UTC
Hi As I already admitted `last` is really an unexpected problem... 8( (Hmm ... maybe there's a way by trying to catch the destruction of the iterator variable... ) Talking about positional subs and leaking I already found a nice workaround by using code-blocks!š 8) `sub noleak (&$) { my $cr=shift; $_[0]=$cr } my @a; for (0..9) { noleak {0,5} my $a; push @a,$a; print $a }` [download] The code-reference seems - as expected - to be precalculated at compile time and is fix! `/usr/bin/perl -w /home/lanx/B/PL/PM/iter_leak.pl CODE(0xa099b48)CODE(0xa099b48)CODE(0xa099b48)CODE(0xa099b48)CODE(0xa09 +9b48)CODE(0xa099b48)CODE(0xa099b48)CODE(0xa099b48)CODE(0xa099b48)CODE +(0xa099b48)` [download] Or do you have an idea to break this approach? Cheers Rolf UPDATE: ARGHH it only works when using fixed values... `sub noleak (&$) { my $cr=shift; $_[0]=$cr } my ($start,$end)=(1,20); my @a; for (0..9) { $start++; noleak {$start,$end} my $a; push @a,$a; print $a }` [download] output `CODE(0x8e29760)CODE(0x8e47ca8)CODE(0x8e47d08)CODE(0x8e47d68)CODE(0x8e4 +7dc8)CODE(0x8e47e28)CODE(0x8e47e88)CODE(0x8e47ee8)CODE(0x8e47f48)CODE +(0x8e47fa8)` [download] ... but commenting out the push produces: `CODE(0x81f7760)CODE(0x81f7760)CODE(0x81f7760)CODE(0x81f7760)CODE(0x81f +7760)CODE(0x81f7760)CODE(0x81f7760)CODE(0x81f7760)CODE(0x81f7760)CODE +(0x81f7760)` [download] and there is no need to propagate the coderef outside the sub... UPDATE š) I ran some tests, better forget it...it really only seems to work reliably with constant values in the code-block ...seems to be an optimization issue. UPDATE I'm going to run some tests with `state`.	[reply] [d/l] [select]