parameters

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

I have a subroutine that needs to take two parameters, a scalar and an array. If I call and define it like this:

&func( $scalar, @array );

sub func {
my $var = shift;
my @list = @_;
# do stuff
}
[download]

Will $var have the value of $scalar and @list the value of @array?

If not, I had considered passing in the parameters as a scalar and a reference to an array. That would go like this

&func ( $scalar, \@array );

sub func {
my $var = shift;
my @list = ???? #what the heck do I put here to get @list == @array?
# do stuff
[download]

Am I correctly passing an array reference into func? And once I do so, how do I get it out again?

Thanks in advance.

JAreallybadPH

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Re: parameters by chipmunk (Parson) on Jan 19, 2001 at 01:51 UTC
Yep, your first code snippet will work just fine. (Did you try it out? :) In your second code snippet, you can get the array back with either of: `my @list = @{ $_[0] }; my @list = @{shift()};` [download] Passing a ref to the array, as in your second snippet, is the way to go if you need to pass in several arrays and keep them distinct in the subroutine.	[reply] [d/l]
(jeffa) Re: parameters by jeffa (Bishop) on Jan 19, 2001 at 01:53 UTC
Yes, always pass an array as a reference when passing multiple arguments to a subroutine. You de-reference the array in the sub like so: `my ($var,$rlist) = @_; # de-reference $rlist like so: @{$rlist} - but, TIMTOWTDI ;) foreach(@{$rlist}) { #do stuff }` [download] UPDATE: Almost forgot about this one: `my $var = shift; my @list = @{+shift}; # you cannot use @{shift}, the + operator tricks perl # into getting the value of shift first` [download] Jeff L-LL-L--L-LL-L--L-LL-L-- -R--R-RR-R--R-RR-R--R-RR F--F--F--F--F--F--F--F-- (the triplet paradiddle)	[reply] [d/l] [select]
Re: parameters by $code or die (Deacon) on Jan 19, 2001 at 02:45 UTC
The first example will work, but as chipmunk says, you should use a reference if you are passing one or more arrays\hashes to a sub, otherwise it gets very difficult. Consider this: `my @fruit = ('apples', 'pears', 'bananas'); my @drinks = ('cola', 'lemonade', 'water'); foo(@fruit,@drinks);` [download] This is not a big problem if the number of entities in @fruit and @drinks is always the same, but suppose there are different amounts of fruit or drinks each time the script runs? With a reference you can do this: `foo(\@fruit,\@drinks); sub foo { my ($fruit,$drinks) = @_; print $fruit->[0], "\n"; print $drinks->[0], "\n"; }` [download] This will print: apples cola References are really useful but a bit daunting at first. Check perlref documentation and dive in and see what happens. $code or die Using perl at The Spiders Web	[reply] [d/l] [select]
Re: parameters by Anonymous Monk on Jan 19, 2001 at 20:37 UTC
The wonderful folks at perlmonks come through again. Thank you very much for all your help. P.S. In case you were wondering why I asked about the first snippet (which was easily testable, as you pointed out), it just seemed a little hack-ish and I wanted to make sure there weren't going to be any unforseen consequences. The real question I wanted to ask was the second one, which seemed a much cleaner implementation (especially if I need to pass in a second array). Thanks again for all of your help, everyone. JAslightlybetterPH	[reply]