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Re^2: Small troubles with references

by injunjoel (Priest)
on Feb 09, 2006 at 21:00 UTC ( #529194=note: print w/replies, xml ) Need Help??

in reply to Re: Small troubles with references
in thread Small troubles with references

Just to help illustrate how Perl 'flattens' or as I try to think of it (thanks to diotalevi) 'list-ifies' subroutine arguments consider the following
#!/usr/bin/perl -w use strict; my @array = qw(arrayval1 arrayval2 arrayval3 arrayval4 arrayval5); my %hash = (key1=>'val1', key2=>'val2', key3=>'val3'); sub check_input_list { print "\n"; print "@_"; print "\n"; } check_input_list(@array, %hash); check_input_list(\@array, %hash); check_input_list(@array, \%hash); check_input_list(\@array, \%hash);
The Output
arrayval1 arrayval2 arrayval3 arrayval4 arrayval5 key2 val2 key1 val1 +key3 val3 ARRAY(0x1824320) key2 val2 key1 val1 key3 val3 arrayval1 arrayval2 arrayval3 arrayval4 arrayval5 HASH(0x182435c) ARRAY(0x1824320) HASH(0x182435c)
Notice in the output of the first call the keys and values from %hash get tacked onto the end of the values in @array as if the entire thing were one huge list. Now imagine trying to get keys or values from %hash? Not likely nor easy.
In the second and third examples we pass one reference but the argument list is still just a list.
The final example is much cleaner. If you were confused about what you originally passed into the sub your could always call ref and find out; otherwise there is no way to tell if you are passed a 'list-ified' hash or array.

"I do not feel obliged to believe that the same God who endowed us with sense, reason and intellect has intended us to forego their use." -Galileo

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