Re: How can I access object data in a user defined sort cmp function?

You can create a closure for the object:

#!/usr/bin/perl
use warnings;
use strict;

use Data::Dumper;

my $self = {
            hash_ref => { item1 => 12,
                          item2 =>  9,
                        },
           };

print Dumper(sort_hash_ref_keys_by_value($self));

sub sort_hash_ref_keys_by_value {
    my $self = shift;
    my $by_value = sub {
        $self->{hash_ref}->{$a} <=> $self->{hash_ref}->{$b}
    };
    return sort $by_value keys %{ $self->{hash_ref} };
}
[download]

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Comment on Re: How can I access object data in a user defined sort cmp function? Download Code

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Re^2: How can I access object data in a user defined sort cmp function? by sundialsvc4 (Abbot) on Jan 28, 2015 at 23:38 UTC
“Schweee-e-ee-t!” An extremely elegant solution. ++ ++ ++ ... And, just for completeness, just for the “technically ~~confused~~ curious” passers-by (however many years from now ...) about “what ~~in the heck~~ a ‘closure’ is,” and with no attempt to steal anyone’s thunder: A closure is ~~voodoo~~ an advanced technique that Perl makes very easy. The local variable named `$by_value` is made to contain a reference to an anonymous `sub` which was created within a block of code in which a local variable named `$self` was “visible” to it, and in which it was known that this `$self` would continue to exist (with its then-present value) for the duration over which it will be needed. (Namely: “the lifetime of `sub sort_hash_ref_keys_by_value`.”) This anonymous `sub` ... a “closure” ... will, rather magically, be able to “see” `$self` too, and can therefore refer to it in addition to `$a` and `$b`. Each time the `sort` verb invokes this anonymous function, that function will magically be able to “see” `$self`, as though the `sort` verb, itself, were also located in the same block of source-code in which the closure-`sub` is defined. The next best thing to being in two places at one time. Masterful. Brilliant.	[reply]
Re^2: How can I access object data in a user defined sort cmp function? by soonix (Canon) on Jan 29, 2015 at 10:04 UTC
A (IMHO very good) explanation of what a closure is → http://simple.wikipedia.org/wiki/Closure_(computer_science)	[reply]


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