Re: Unusual Closure Behaviour

Well, technically what is happening is not violating Camel III. See, it *does* get its own scratchpad, which can be quickly checked by:

    #!/opt/perl/bin/perl -w
    use strict;
    sub foo;
    sub foo {
        return unless $_ [0];
        my $x if 0;
        print ++ $x, " ";
        foo $_ [0] - 1;
    }
    
    foo 1; print "\n";
    foo 2; print "\n";
    foo 3; print "\n";
    foo 4; print "\n";
    __END__
    1 
    2 1 
    3 2 1 
    4 3 2 1
[download]

Scary, isn't? When the subroutine recurses, it notices there is still a reference to $x and hence it will create a new scratchpad. But when there is no reference, it will reuse an old scratchpad....

I do agree that using my in this way doesn't tend to lead to well understood code. I wouldn't go as far as to say it's never useful, but such cases will be very rare and it's not a technique I would teach in my classes.

-- Abigail

Comment on Re: Unusual Closure Behaviour Select or Download Code

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Re^2: Unusual Closure Behaviour by BrowserUk (Patriarch) on Sep 12, 2015 at 23:55 UTC
Come back Abigail (II). This place needs you.	[reply]
Re^3: Unusual Closure Behaviour by shmem (Chancellor) on Sep 13, 2015 at 09:14 UTC
This place needs you. So true. What happens here? Does this mean that each scratchpad is persistent at its recursion level? `use strict; sub foo; sub foo { return unless $_ [0]; my $x if undef; print ++ $x, " "; foo $_ [0] - 1; } foo 1; print "\n"; foo 2; print "\n"; foo 3; print "\n"; foo 7; print "\n"; foo 11; print "\n"; foo 9; print "\n"; foo 15; print "\n"; __END__ 1 2 1 3 2 1 4 3 2 1 1 1 1 5 4 3 2 2 2 2 1 1 1 1 6 5 4 3 3 3 3 2 2 7 6 5 4 4 4 4 3 3 2 2 1 1 1 1` [download] perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'	[reply] [d/l]
Re^2: Unusual Closure Behaviour by Anonymous Monk on Sep 12, 2015 at 23:24 UTC
Have you tried this? `#!/usr/bin/perl use strict; sub foo; sub foo { return unless $_ [0]; my $x if undef; print ++ $x, " "; foo $_ [0] - 1; } foo 29; print "\n";` [download] It prints: 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Hum...	[reply] [d/l]
Re^3: Unusual Closure Behaviour by Anonymous Monk on Sep 13, 2015 at 05:27 UTC
`Deprecated use of my() in false conditional at - line 6.`	[reply] [d/l]


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