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

Hi all,

I need you'r help for a specific issue.

My problem :

I need to access to an attribute path into an object. Here a typical example :

my $objectWhenceFindPath;
$objectWhenceFindPath->{here}->{an}->{hypothetical}->{path} = "some va
+lue";

my @path = ("an", "hypothetical", "path");

my $currentPath = $objectWhenceFindPath->{here};
for my $index (0 .. ($#path - 1)) {
    $currentPath = $currentPath->{$path[$index]};
    # Some logic, or not. Depend of script.
}
$currentPath ++;

[download]

At this time, I have not find any solutions to do this. Note as functional, the $objectWhenceFindPath is retrieved from an object subroutine.

Tested solution :

Many thanks to anyone able to purpose a solution.

Replies are listed 'Best First'.
Re: Object attribute follower
by Corion (Patriarch) on Apr 14, 2016 at 19:52 UTC
[reply]

      Seem to be the solution. I'll try this tomorrow and come back for test results.

      Many thanks Corion .

[reply]
Re: Object attribute follower
by kcott (Archbishop) on Apr 15, 2016 at 04:41 UTC

    G'day CSmatthieu,

    Welcome to the Monastery.

    Here's a highly contrived example of how you might pass a hashref (e.g. your object), an arrayref (e.g. your attribute path), and a coderef (e.g. your logic) to a single subroutine. 

    #!/usr/bin/env perl -l

use strict;
use warnings;

my %data = (
    A => { C => { D => 4, E => [ 22, 33 ], }, },
    B => { C => { D => [ 44, 55 ], E => 5, }, },
);

my $get_value_code = sub { $_[0] };
my $is_ref_code = sub { ref $_[0] };

my @paths = ([qw{A C D}], [qw{A C E}], [qw{B C D}], [qw{B C E}], []);

for (@paths) {
    if (generic_hash_logic(\%data, $_, $is_ref_code)) {
        print "Path [@$_] is a reference: not printed.";
    }
    else {
        print "Path [@$_] is a value: ", 
            generic_hash_logic(\%data, $_, $get_value_code);
    }
}

sub generic_hash_logic {
    my ($hash, $path, $code) = @_;

    my $end = $hash;

    $end = $end->{$_} for @$path;

    $code->($end);
}

    [download]

    Output:

    Path [A C D] is a value: 4
Path [A C E] is a reference: not printed.
Path [B C D] is a reference: not printed.
Path [B C E] is a value: 5
Path [] is a reference: not printed.

    [download]

    As I said, this is highly contrived and only intended to show a technique (i.e. it's not a solution).

    By putting your equivalent of &generic_hash_logic in a module, you can share it amongst all your scripts: no need to "create a subroutine for each one".

    — Ken

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