How to add a scalar value (string) to an existing hash in Perl - perl

Question

I just want to know what the process is behind merging a value into a hash.
I have a hash which has 5 to 6 keys depending on if the error outputs runtime values. The method that takes in the arguments also take an error message string in first, also. I want it to be able to add this error message string into the hash, to make one big hash basically.
This is how the method would be called:
ASC::Builder::Error->new("Simple error message here", code => "UNABLE_TO_PING_SWITCH_ERROR", switch_ip => $ip3, timeout => $t1);
The last two values assign runtime parameters/values to keys inside the context key in the error hash.
Here is a look at the error hash:
use constant ERROR_CODE => {
UNABLE_TO_PING_SWITCH_ERROR => {
category => 'Connection Error',
template => 'Could not ping switch %s in %s seconds.',
context => [qw(switch_ip timeout)],
tt => {template => 'disabled'},
fatal => 1,
wiki_page => 'www.error-solution.com/ERROR_CODE_A',
}
};
Here is my method to manipulate the error hash and construct the message
sub _create_error_hash {
my $error_string = shift; if(defined($params{code}) {
my $first_param = delete $params{code};
foreach my $key (#{$first_param->{context}}) {
$first_param->{$key} = $key;
}
my #template_args = map { $first_param->{$_}} #{$first_param->{context} };
$first_param->{message} = sprintf($first_param->{template}, #template_args); }
return bless $first_param;
}
sub _merge_hashes {
my ($message = {message => $messsage}, $first_param = {first_param => $first_param}) = # _;
#merge these two hashes and bless into $class (don't know how to merge hashes)
my %merged_hash = ($message, $first_param);
return bless $merged_hash, $class;
}
The output of _create_hash should be the input for _merge_hashes
Not sure if I have handled that properly. These methods will be use inside the new method (which is a mess right now) hence why it's not included.
That's just an attempt , of an example I seen on perlmonks, Here is the link:
http://www.perlmonks.org/?node_id=14263

Answer 1

I'm going to start with the simple explanation of how to merge a hash in perl, it's pretty simple.
use strict;
use warnings;
use Data::Printer;
my (%a, %b, %c);
%a = (a => 1, b => 2);
%b = (a => 0, c => 3, d => 4);
%c = (%a, %b);
p(%c); # { a => 0, b => 2, c => 3, d => 4 }
You'll note with the a keys that if there are duplicates whatever value appears in the second set will be the one that 'wins'.
I honestly have no idea what that second function is doing because it references variables that don't exist on practically every line. (The create one also does this but only on a couple lines).
From your description I think you only want a single key added so you don't really need to do that though, you should be able to just add the key to the original object: $error->{messsage} = $message
But assuming you did want to pass two hash references in and merge them, it would look something like this:
sub merge {
my ($first, $second) = #_;
my %merged = (%$first, %$second);
return bless \%merged, $class;
}