How Do I pass a hash to a subroutine?

filmo has asked for the wisdom of the Perl Monks concerning the following question: ⭐ (hashes)

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Re: How Do I pass a hash to a subroutine?⭐ by MeowChow (Vicar) on Feb 26, 2001 at 05:15 UTC
Hashes can be passed either by value: `mysub(%hash); sub mysub { my (%params) = @_; }` [download] or by reference: `mysub(\%hash); sub mysub { my $params = shift; my %paramhash = %$params; }` [download] Each approach has it's advantages and disadvantages. Pass-by-value offers a simpler syntax, while pass by reference is faster and more flexible, allowing you to easily intermingle the hash with other parameters.	[reply] [d/l] [select]
Re: How Do I pass a hash to a subroutine?⭐ by Doraemon (Beadle) on May 11, 2004 at 13:43 UTC
And, if you need to pass multiple parameters (eg. a hash and then an array) pass by reference; otherwise the hashes and arrays are flattened into a single list and the sub can't tell what is part of which. Here is an example of using prototypes to force a pass-by-reference. `sub foo(\%\@) { my ($hash_ref, $array_ref) = @_; #... } foo (%hash, @array);` [download]	[reply] [d/l]
Re: How Do I pass a hash to a subroutine?⭐ by nite_man (Deacon) on Feb 13, 2003 at 12:22 UTC
Also, you can use prototypes to get special argument passing: `my_sub(%hash) sub my_sub(\%) { my $hash_ref = shift; map { print "$_ => $$hash_ref{$_} \n" } keys %$hash_ref; }` [download]	[reply] [d/l]
Re: How Do I pass a hash to a subroutine? by thephpguy (Initiate) on May 06, 2011 at 18:06 UTC
MeowChow's code for passing by reference is VERY inefficient unless you actually want a copy of the Hash. (Why pass by ref if you want a copy?) `mysub(\%hash); sub mysub { my $paramhash = $_[0]; }` [download] With the above code any modification will affect the original hash.	[reply] [d/l]
Re: How Do I pass a hash to a subroutine? by GoldenSage (Initiate) on Nov 28, 2012 at 21:41 UTC
New here, maybe more of an explaination of prototypes? Tried to use your routine of (\%) which had syntax error at the line (also created syntax errors along every @_ line called in the library I'm writting. Looked at prototypes (first time I've seen such) at Prototypes. Hasn't made since yet, appears certain functions being called. Does look like a neat solution if it works for me. Originally posted as a Categorized Answer.	[reply]
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