Last night I was experimenting with XML::Parser, trying to parse an XML document. I encountered what I consider to be a pretty strange syntax/context oddity. 
my @array = qw(foo bar); 
while (my ($attrib, $value) = each (@array) ) { 
  print "$attrib=$value\n"; 
}

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produces the error message:
Type of arg 1 to each must be hash (not private array) at test.pl line 2, near "@array) "

Peculiar, I thought--why can't the array be "automagically" converted to a hash? But anyway.... I know I can create a hash by assigning an array to a hash, and although each requires a HASH, I thought any expression that evaluates to a hash would be ok. So I try the following code: 

my @array = qw(foo bar); 
while (my ($attrib, $value) = each (my %hash = @array) ) { 
  print "$attrib=$value\n"; 
}

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I expected that to work: surely the my %hash = @array code is evaluated first, resulting in a hash. But this code didn't work either, I got the error:
Type of arg 1 to each must be hash (not list assignment) at test.pl line 2, near "@array) "

So I decided to insert another line before the while statement, as shown below: 

my @array = qw(foo bar); 
my %hash = @array; 
while (my ($attrib, $value) = each (%hash) ) { 
  print "$attrib=$value\n"; 
}

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This did finally have the desired effect, but it seems incredibly redundant and un-Perl-like to have to have the array to hash assignment as a separate statement. Obviously if I want to create a hash, perl needs to create a hash table to do the look-ups so hashes aren't identical to arrays, but it seems strange that it can't automatically do this, especially when many Perl operators and functions act in magical ways (e.g. the ++ operator on strings).

In reply to 'each' syntax oddity? by SuperCruncher

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