in reply to How to distinct the call position of a sub?

And caller() doesn't help? 
my ($package, $file, $line, $subname, $hasargs, ...) = caller();

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I'd think that the combination of $package, $line, and $subname ought to be pretty specific.....

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Re^2: How to distinct the call position of a sub?
by Limbic~Region (Chancellor) on Nov 24, 2008 at 20:17 UTC
    Old_Gray_Bear,
    I would agree with the caveat that it would likely fail to DWIM in many situations. Assuming way too much about how LanX will use it, the following seems to work: 
    #!/usr/bin/perl
use strict;
use warnings;

{
    my %seen;

    sub iter {
        my ($beg, $end, $by) = @_;

        my $key = join '*', caller();

        return $seen{$key}->() if $seen{$key};

        my $pos = $beg - $by;

        $seen{$key} = sub {
            $pos += $by;
            if ($pos > $end) {
                delete $seen{$key};
                return;
            } 
            return $pos;
        };

        return $seen{$key}->();

    }
}

while (my $x = iter(1, 10, 1)) {
    print "$x\n";
    while (my $y = iter(1, 10, 1)) {
        print "$x - $y\n";
    }
}

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    Update: In some versions of perl (5.8.8 and 5.10.0 reported in the CB), an infinite loop results if you delete the print "$x\n"; line. It seems that unless there is some executable statement between the two while loops, caller reports them as happening on the same line. While I think this is a bug in perl, it also shows why this is not a good solution. Running perl -MO=Deparse doesn't seem to support why perl believes they are on the same line.

    Cheers - L~R

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      Seems to be rather fragile... i.e. for me it works with Perl 5.10.0 if you leave in the print "$x\n"; (without it, I can replicate the infinite loop), but with Perl 5.8.8, the iterator returns the wrong values (with and without the print "$x\n"; — no infinite loop here, though):

      Read more... (900 Bytes)
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Re^2: How to distinct the call position of a sub?
by LanX (Saint) on Nov 24, 2008 at 20:45 UTC
    Well ... would you publish a syntax extension with the footnote "but never use it in the same line!" ?

    And beside this, iterator are just an example for a general problem to know "which call is this".

    Think about a position sensitive function you want to call twice within a ternary operator ... "never use it in the same line?"

    And even when I publish it with this restriction, I have no means to throw an error-message if used in a wrong way.

    So if there is a general clean solution, where else should I try to ask for wisdom?
    And shouldn't I ask before implementing an imperfect solution? 8 )

    Cheers Rolf

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      And beside this, iterator are just an example for a general problem to know "which call is this".

      I don't think there's a reliable solution, which is why I think any design based on having this information is flawed. What do you expect to get if you're called from string eval?

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        > What do you expect to get if you're called from string eval?

        what do you expect when you call foreach from string eval?
        Well you bring a good argument against using the linenumber from caller.

        Cheers Rolf

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