Re: How to declare a hash of array?

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Re^2: How to declare a hash of array? by bart (Canon) on Sep 29, 2007 at 10:35 UTC
But careful with mixed data structures and the risk of accidental symbolic references. strict can catch that. An example: `my %hash; $hash{beta} = 'x'; for my $name ( qw(alpha beta) ) { push @{$hash{$name}}, 123, 456; } use Data::Dumper; print Dumper \%hash;` [download] Result: `$VAR1 = { 'alpha' => [ 123, 456 ], 'beta' => 'x' };` [download] So... where's the array data for 'beta'? It's in the global variable @x. Witness: append this line to the above script: `print Dumper \@x;` [download] Result: `$VAR1 = [ 123, 456 ];` [download] With strict enabled, it'll get caught while trying to push the data: insert the line `use strict;` [download] at the top of the script and comment out the line, dumping @x, we appended earlier: `Can't use string ("x") as an ARRAY ref while "strict refs" in use at t +est.pl line 6.` [download] Nasty if you didn't expect it. The risk of running into it is greatest when using data structures of unequal depth.	[reply] [d/l] [select]

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Re^2: How to declare a hash of array?
by bart (Canon) on Sep 29, 2007 at 10:35 UTC

An example:

my %hash;
$hash{beta} = 'x';
for my $name ( qw(alpha beta) ) {
    push @{$hash{$name}}, 123, 456;
}

use Data::Dumper;
print Dumper \%hash;
[download]

$VAR1 = {
          'alpha' => [
                       123,
                       456
                     ],
          'beta' => 'x'
        };
[download]

print Dumper \@x;
[download]

$VAR1 = [
          123,
          456
        ];
[download]

With strict enabled, it'll get caught while trying to push the data: insert the line

use strict;
[download]

Can't use string ("x") as an ARRAY ref while "strict refs" in use at t
+est.pl line 6.
[download]

Nasty if you didn't expect it.

The risk of running into it is greatest when using data structures of unequal depth.

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