Perl hash, array and references - perl

Question

I have this 3 lines of code in a sub and I'm trying to write them together on one line only.. but I'm quite lost
my %p = #_;
my $arr = $p{name};
my #a = #$arr;
what's the correct way of doing this?
thank you!

Answer 1

my %p = #_;
#_ is assumed to contain key-value pairs which are then used to construct the hash %p.
my $arr = $p{name};
The argument list is assumed to have contained something along the lines of name, [1, 2, 3,] so that $p{name} is an reference to an array.
my #a = #$arr;
Dereference that array reference to get the array #.
Here is an invocation that might work with this prelude in a sub:
func(this => 'that', name => [1, 2, 3]);
If you want to reduce the whole prelude to a single statement, you can use:
my #a = #{ { #_ }->{name} };
as in:
#!/usr/bin/env perl
use strict;
use warnings;
use YAML::XS;
func(this => 'that', name => [1, 2, 3]);
sub func {
my #a = #{ { #_ }->{name} };
print Dump \#a;
}
Output:
---
- 1
- 2
- 3
If the array pointed to by name is large, and if you do not need a shallow copy, however, it may be better to just stick with references:
my $aref = { #_ }->{ name };

Answer 2

OK so what you're doing is:
Assign a list of elements passed to the sub, to a hash.
extract a value from that hash (that appears to be an array reference)
dereference that into a standalone array.
Now, I'm going to have to make some guesses as to what you're putting in:
#!/usr/bin/perl
use warnings;
use strict;
use Data::Dumper;
sub test {
my %p = #_;
my $arr = $p{name};
my #a = #$arr;
print Dumper \#a;
}
my %input = ( fish => [ "value", "another value" ],
name => [ "more", "less" ], );
test ( %input );
So with that in mind:
sub test {
print join "\n", #{{#_}->{name}},"\n";
}
But actually, I'd suggest what you probably want to do is pass in the hashref in the first place:
#!/usr/bin/perl
use warnings;
use strict;
use Data::Dumper;
sub test {
my ( $input_hashref ) = #_;
print Dumper \#{$input_hashref -> {name}};
}
my %input = ( fish => [ "value", "another value" ],
name => [ "more", "less" ], );
test ( \%input );
Also:
Don't use single letter variable names. It's bad style.
that goes double for a and b because $a and $b are for sorting. (And using #a is confusing as a result).