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Re^2: Autovivification sucking the life out of me

by shenme (Priest)
on Oct 14, 2005 at 06:48 UTC ( #500140=note: print w/ replies, xml ) Need Help??


in reply to Re: Autovivification sucking the life out of me
in thread Autovivification sucking the life out of me

I think you missed the point of the post, which is "how is the variable $ENV{TMPDIR} being autovivified?" I am not caring that the value passed into the subroutine is undefined, since the environment variable is indeed not defined. But I do care that the variable outside the subroutine changes from '<absent>' to '<undef>'.


Comment on Re^2: Autovivification sucking the life out of me
Re^3: Autovivification sucking the life out of me
by pg (Canon) on Oct 14, 2005 at 06:54 UTC

    Update: My apologies! Forget what I have said, it was my observation was off, not yours. But it might be a better idea to demo your issue by using Data::Dumper.

    use Data::Dumper; use strict; use warnings; my %foo = ( BAZ => 1 ); sub see_args { }; print Dumper(\%foo); see_args( @foo{qw(BAR BAZ)} ); print Dumper(\%foo);

    It prints:

    $VAR1 = { 'BAZ' => 1 }; $VAR1 = { 'BAZ' => 1, 'BAR' => undef };

    Yes, autovivification is in working.

    Your observation was off. In your original post, you were confused by the fact that the $ENV{TMPDIR} "appears" to have a value as you saw it through that sprintf. No, you didn't see the value of $ENV{TMPDIR}. Your sprintf printed a constant "<absent>", not the value of $ENV{TMPDIR}.</strick>

      A simpler example perhaps:
      use strict; use warnings; my %foo = ( BAZ => 1 ); sub see_args { }; warn sprintf "at start: BAR '%s'\n", ! exists $foo{BAR} ? '<absent>' : ! defined $foo{BAR} ? '<und +ef>' : $foo{BAR}; # see_args( @foo{qw(BAR BAZ)} ); my @a = @foo{qw(BAR BAZ)}; warn sprintf "at end: BAR '%s'\n", ! exists $foo{BAR} ? '<absent>' : ! defined $foo{BAR} ? '<und +ef>' : $foo{BAR};

      Running this without the subroutine call, but rather the assignment to the array, results in output:

      at start: BAR '<absent>' at end: BAR '<absent>'
      That is, using the slice @foo{qw(BAR BAZ)} returns the values without modifying them.

      Commenting out the assignment and instead executing the subroutine call produces this output:

      at start: BAR '<absent>' at end: BAR '<undef>'
      Somehow using the slice in the call to the subroutine has modified the values in the slice, creating an undef value for the key 'BAR'. How?

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