In Java, constructors are named the same thing as the package they are part of, so objects are created like this:

Object obj = new Object( param1, param2 );

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You can get a similar syntax using Perl's indirect object syntax (though this syntax should probably be avoided):

my $obj = new Object( $param1, $param2 );

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With a trick using the Exporter, we can get rid of the new completely. Here's an example:

package Constructor;
use strict;
use warnings;
use Exporter;

BEGIN {
        our @ISA;
        push @ISA, 'Exporter';

        our @EXPORT     = qw( );
        our @EXPORT_OK  = qw( );
}


sub import 
{
        my $class = shift;
        my ($package, $filename, $line) = caller;

        no strict 'refs';
        my $slot = $package . '::' . $class;
        # Input fields to our constructor
        my @FIELDS = qw( foo bar baz );
        *$slot = sub {
                my $in_class = shift;
                my $params;
                if(ref($in_class) eq 'HASH') {
                        $params    = $in_class;
                        $in_class  = $class;
                }
                else {
                        $params = shift || { };
                }

                my $self = { map { $_ => $params->{$_} || '' } @FIELDS
+ };
                bless $self, $class;
        };
}

1;

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Here's a one-liner that demonstrates its use:

$ perl -MData::Dumper -I. -MConstructor -le '$obj = Constructor({ foo 
+=> 1 }); print Data::Dumper::Dumper($obj);'
$VAR1 = bless( {
                 'bar' => '',
                 'baz' => '',
                 'foo' => 1
               }, 'Constructor' );

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Of course, this is an export-by-default in disguise. It is probably better if the import() routine allowed for conditional importing of this syntax. Doing this is left as an exercise to the reader.

I also forgo any promises that this will be readable in real-world programs :)

----
I wanted to explore how Perl's closures can be manipulated, and ended up creating an object system by accident.
-- Schemer

:(){ :|:&};:

Note: All code is untested, unless otherwise stated

In reply to Constructors Without ->new() by hardburn

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