Is it possible to use an object as a hash key?
For example, the following code allows me to use an instance of MyClass as a key but when I iterate over the keys and attempt to invoke the get_value
method, I get the error:
Can't locate object method "get_value" via package "MyClass=HASH(0x12a4040)" (perhaps you forgot to load "MyClass=HASH(0x12a4040)"?)
package MyClass;
use strict;
sub new
{
my $class = shift;
my $self = {
_value => shift
};
bless $self, $class;
return $self;
}
sub get_value {
my($self) = @_;
return $self->{_value};
}
my %hash = ();
%hash->{new MyClass(1)} = 0;
%hash->{new MyClass(2)} = 1;
for my $key (keys %hash)
{
print $key->get_value;
}
Can you use objects as Object keys in JavaScript? # The short answer is "no". All JavaScript object keys are strings.
One of the most important differences between Ruby and JavaScript is in how they handle the composite data structures. Ruby does this with the hash, while JS calls its version an object. Ruby's hash and JavaScript's object do roughly the same thing—they both represent a collection of values accessed using keys.
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By default, all hash keys in Perl are strings, so what is happening in you code (which has other problems as well), is you are converting the object to a string and storing the string.
In general, if you want to use a object as a key, the simplest way to do it is to use two data structures, one that holds your objects (an array), and another that maps the objects to some values (a hash). It is also possible to create a tied hash which will support objects as keys, but in general, tied hashes are going to be slower than simply using two data structures.
The standard module Tie::RefHash provides a mechanism for using objects (and other references) as hash keys (that work properly when you get them back).
use Tie::RefHash;
tie my %hash, 'Tie::RefHash';
$hash{MyClass->new(1)} = 0; # never use the indirect object syntax
....
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