Re: Re: push undefined and vivification

in use strict it's right. but without, the code:

use Data::Dumper;

@a=('bar');
print Dumper(\@a);

push @{$a[0]}, "foo";

print Dumper(\@a);
print Dumper(\@bar);
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actually append 'foo' to @bar:

$VAR1 = [
          'bar'
        ];
$VAR1 = [
          'bar'
        ];
$VAR1 = [
          'foo'
        ];
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in that case, so, perl do one of three things:

append to the array named by the value of $a[0], or

append to the array-ref in $a[0], or

create an anonymous array and put the reference in $a[0]
in use strict; the behavior of push is predictable, but without -- and using a string in $a[0] -- the behavior is not predictable.

this may be a good reason to use strict, without perl may use the @{$something} as array-ref or variable name... a bit confusing, doesn't it?

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Re: Re: Re: push undefined and vivification by Anonymous Monk on Jan 18, 2004 at 12:53 UTC
`in use strict; the behavior of push is predictable, but without -- and using a string in $a[0] -- the behavior is not predictable` Wrong. The behaviour is perfectly predictable. Observe `use Data::Dumper; @a = 'bar'; @bar = 6; warn push @{$a[0]}, 7; warn Dumper( \@a, \@bar ); warn push @{"$a[0]"}, 8; warn Dumper( \@a, \@bar ); warn push @{"bar"}, 9; warn Dumper( \@a, \@bar ); undef $a[0]; warn push @{$a[0]}, 11; warn Dumper( \@a, \@bar ); __END__ 2 at - line 4. $VAR1 = [ 'bar' ]; $VAR2 = [ 6, 7 ]; 3 at - line 7. $VAR1 = [ 'bar' ]; $VAR2 = [ 6, 7, 8 ]; 4 at - line 10. $VAR1 = [ 'bar' ]; $VAR2 = [ 6, 7, 8, 9 ]; 1 at - line 13. $VAR1 = [ [ 11 ] ]; $VAR2 = [ 6, 7, 8, 9 ];` [download] without perl may use the @{$something} as array-ref or variable name... a bit confusing, doesn't it? Why? Observe `@a = 'bar'; @bar = 6; warn 'PUSHING ONTO @BAR' if defined $a[0]; push @{$a[0]}, 'bar'; undef $a[0]; warn 'PUSHING ONTO $a[0]' if not defined $a[0]; push @{$a[0]}, 'bar'; use Data::Dumper; warn Dumper( \@a, \@bar ); __END__ PUSHING ONTO @BAR at - line 4. PUSHING ONTO $a[0] at - line 10. $VAR1 = [ [ 'bar' ] ]; $VAR2 = [ 6, 'bar' ];` [download]	[reply] [d/l] [select]

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Re: Re: Re: push undefined and vivification
by Anonymous Monk on Jan 18, 2004 at 12:53 UTC

in use strict; the behavior of push is predictable, but without -- and using a string in $a[0] -- the behavior is not predictable

use Data::Dumper;
@a = 'bar';
@bar = 6;
warn push @{$a[0]}, 7;
warn Dumper( \@a, \@bar );

warn push @{"$a[0]"}, 8;
warn Dumper( \@a, \@bar );

warn push @{"bar"}, 9;
warn Dumper( \@a, \@bar );
undef $a[0];
warn push @{$a[0]}, 11;
warn Dumper( \@a, \@bar );
__END__
2 at - line 4.
$VAR1 = [
          'bar'
        ];
$VAR2 = [
          6,
          7
        ];
3 at - line 7.
$VAR1 = [
          'bar'
        ];
$VAR2 = [
          6,
          7,
          8
        ];
4 at - line 10.
$VAR1 = [
          'bar'
        ];
$VAR2 = [
          6,
          7,
          8,
          9
        ];
1 at - line 13.
$VAR1 = [
          [
            11
          ]
        ];
$VAR2 = [
          6,
          7,
          8,
          9
        ];
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without perl may use the @{$something} as array-ref or variable name... a bit confusing, doesn't it?

@a = 'bar';
@bar = 6;

warn 'PUSHING ONTO @BAR' if defined $a[0];

push @{$a[0]}, 'bar';

undef $a[0];

warn 'PUSHING ONTO $a[0]' if not defined $a[0];

push @{$a[0]}, 'bar';

use Data::Dumper;
warn Dumper( \@a, \@bar );

__END__
PUSHING ONTO @BAR at - line 4.
PUSHING ONTO $a[0] at - line 10.
$VAR1 = [
          [
            'bar'
          ]
        ];
$VAR2 = [
          6,
          'bar'
        ];
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