I was tinkering with item-by-item deletion of hashes, looking for something yet unsaid about Hash Entry Deallocation. Investigating the form while (%hash) {delete...}, I found behavior I hadn't expected. The seemingly sane, 

my %foo;
@foo{qw/ foo bar baz /} = 1 .. 3;
while (%foo) {
    my $key = each %val;
    my $val = delete $foo{$key};
    printf "%s => %s is gone.\n", $key, $val;
}

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continues to spin after the hash is depleted, endlessly printing ' => is done.'.

The ugly variation, 

my %foo;
@foo{qw/ foo bar baz /} = 1 .. 3;
my @keys = keys %foo; 
while (%foo) {
    my $key = shift @keys;
    my $val = delete $foo{$key};
    printf "%s => %s is gone.\n", $key, $val;
}

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works as expected.

I first suspected that modifying the hash upset each's bookkeeping, but then how could the more conventional, 

while (my ($key, $val) = each %hash) {
    delete $hash{$key};
    printf "%s => %s is gone.\n", $key, $val;
}

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work?

Does anyone know why this happens?

After Compline,
Zaxo

In reply to Unexpected persistence with each hash by Zaxo

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