For an iterator to work in Perl one needs to initialize it properly

use strict;
use warnings;
use Data::Dump qw/pp dd/;

for my $limit (reverse 1..5) {
    for ( my $iter = countdown($limit); $iter->(my $a) ; ) {
        print "$a: ";
    }
    print "\n";
    
}

sub countdown{
    my $val = shift;

    my $iter = sub {
        if ($val--) {
            $_[0]=$val;
            return 1;
        }
        return;                         # stop iteration
    };

    return $iter;

}
[download]

4: 3: 2: 1: 0: 
3: 2: 1: 0: 
2: 1: 0: 
1: 0: 
0:
[download]

(I used c-style for here for clarity*)

But I'd rather like to stay DRY and to write something like

while ( countdown $limit => my $a ) {
    ....
}
[download]

Where countdown can elaborate if the loop is (re)entered and does the init step automatically.

NB: Other languages have this feature for so called iterator objects.

I'm wondering if this could be tricked into Perl without XS wizardy °...

Approaches ...

• I tried %^H , but this seems to be a compile time effect only.
• Blessing a DESTROY method to \$a doesn't help, because it's triggered for all iterations not only the first.
• I was thinking to use PadWalker to inject a var with a DESTROY hook into closed_over , but I doubt this has a chance to work.
• UPDATE: Well with Keyword::Simple I could define a new loop keyword which expands into for(;;;)
• UPDATE: there is some magic connected to the diamond operator <$obj> which can be overloaded, but you can't use it with functions because the syntax is convoluted with file-glob.

IDEAS?

*) please note that while(CODE){} and for(;CODE;){} have the same effect.

°) many issues could be solved like this...

update

The countdown iterator was used for demonstration only, I now plenty of ways to countdown. Iterators are a general issue.

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