Modify array of hashes by reference - arrays

Question

I want to modify an array of hashes by a sub function, therefore I want to handover the array by reference, de-reference in the sub function and modify it furthermore.
After this modification, the array shall hold the modified values instantly, I don't want to explicitely return the modified hash (want to work on the original array).
Unfortunately I do not succeed with that. There are many web hints concerning access to references of array of hashes, but I couldn't find one which manipulates the array.
my #array_of_hashes = ( {name => "Alice"},
{name => "Bob"} );
my $myhashref = \%{$array_of_hashes[0]}; # This holds a ref to {name=>"Alice"}
my %myhash = %{$myhashref}; # De-reference, shall be the Hash to work on
print $myhash{name} . "\n"; # This shows Alice
$myhash{age}=32; # Want to add 'age' to the Alice Hash, does not work
This modified hash does not show {age}. When you have a look at #array_of_hashes with print Data::Dump::dump(#array_of_hashes) the line $myhash{age}=32; has no impact on #array_of_hashes.
How can I hand over a reference to e.g. the first element of #array_of_hashes to a function and how to I have to dereference it in the function in order to be able to modify the hash within #array_of_hashes?

Answer 1

You said: I want to modify an array of hashes by a sub function
If I understand right, something like the following could work:
use 5.014;
use warnings;
use Data::Dumper;
my #aoh = (
{name => "Alice"},
{name => "Bob"}
);
do_some(\#aoh); #pass arrayref
$aoh[1]->{text} = 'huhu';
say Dumper \#aoh;
say "$aoh[1]->{name} has age $aoh[1]->{age} and says $aoh[1]->{text}";
sub do_some {
my $ar = shift;
for my $hr (#$ar) { #for each array element
$hr->{age} = int rand 100;
}
}
# however (IMHO)
# using arrayref from the beginning is more cleaner
my $aohr = [
{name => "Alice"},
{name => "Bob"}
];
do_some($aohr);
$aohr->[0]->{text} = 'juju';
say Dumper $aohr;
say "$aohr->[0]->{name} has age $aohr->[0]->{age} and says $aohr->[0]->{text}";
#could use the shortened form
#say "$aohr->[0]{name} has age $aohr->[0]{age} and says $aohr->[0]{text}";
the above produces for example:
$VAR1 = [
{
'age' => 31,
'name' => 'Alice'
},
{
'age' => 10,
'text' => 'huhu',
'name' => 'Bob'
}
];
Bob has age 10 and says huhu
$VAR1 = [
{
'name' => 'Alice',
'age' => 94,
'text' => 'juju'
},
{
'name' => 'Bob',
'age' => 57
}
];
Alice has age 94 and says juju

Answer 2

You already created a ref to each hash when you create the array. then you defrencing the hash and allocating it to a new hash varible.
my %myhash = %{$myhashref}; # De-reference, shall be the Hash to work on
So you now have a new hash which was created as a copy of the alice hash. However the new hash and the alice hash are seperate. you then modify the new hash works ok but it will not be reflected in the alice hash as they are seperate. instead you should modify the existing hash ref. For example try below.
use strict;
use warnings;
use Data::Dumper;
my #array_of_hashes = ( {name => "Alice"},
{name => "Bob"} );
print $array_of_hashes[0]->{'name'}, "\n";#this shows alice
$array_of_hashes[0]->{'age'}=32; # Want to add 'age' to the Alice Hash, does not work
print Dumper \#array_of_hashes;