Perl - call an instance of a class

Question

Is there way to catch the event of calling an instance of a Perl class?

my $obj = ExampleClass->new();
$obj(); # do something without producing error
         


        

Answer 1

Overloading "&{}" is obviously the way to go, but you could base your object on a sub instead of the commonly-preferred hash.

ExampleClass.pm:

package ExampleClass;

use strict;
use warnings;
use feature qw( current_sub say );

my %objects;

sub new {
   my $class = shift;
   my $dummy;  # Force each evaluation of sub{} to return a new variable.
   my $self = bless(sub { $dummy if 0; __SUB__ ->__call__(@_) }, $class) }, $class);
   my $inner = $objects{$self} = {};
   return $self;
}

sub DESTROY {
   my $self = shift;
   delete($objects{$self});
}

sub __call__ {
   my $inner = $objects{ my $self = shift };
   say "__call__(".join(", ", @_).")";
}

sub some_attribute {
   my $inner = $objects{ my $self = shift };
   if (@_) { $inner->{some_attribute} = $_[0]; }
   return $inner->{some_attribute};
}

1;

The main program:

#!/usr/bin/perl

use strict;
use warnings;
use feature qw( say );

use ExampleClass qw( );

{
   my $obj = ExampleClass->new();

   $obj->some_attribute("value");
   say $obj->some_attribute();

   $obj->(qw( a b c ));
}

{
   my $obj1 = ExampleClass->new();
   $obj1->some_attribute("value1");

   my $obj2 = ExampleClass->new();
   $obj2->some_attribute("value2");

   say $obj1->some_attribute();
   say $obj2->some_attribute();
}

Output:

value
__call__(a, b, c)
value1
value2

This is basically what's called an "inside-out" object.