Re^5: Designing a DWIMish interface for generator function

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]

Comment on Re^5: Designing a DWIMish interface for generator function Select or Download Code

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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]

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Re^6: Designing a DWIMish interface for generator function
by LanX (Saint) on Feb 01, 2010 at 11:12 UTC

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]