Perl UNIVERSAL

All blessed references inherit from UNIVERSAL:

• Checking the type of a reference:

  $obj->isa(TYPE)
  CLASS->isa(TYPE)
  isa(VAL, TYPE)
  

• Checking for the existence of a function:

  $obj->can(METHOD)
  CLASS->can(METHOD)
  can(VAL, METHOD)
  

• Example for the above:

  #!/usr/bin/perl
  
  use strict;
  use warnings;
  
  if (not Test->can('new')) {
      die 'do not know how to create an object of type "Test"' . "n";
  }
  
  my $obj = Test->new();
  
  if ($obj->isa('Test')) {
      print '$obj is a "Test"' . "n";
  }
  if ($obj->can('print')) {
      print '$obj can "print"' . "n";
  }
  
  package Test;
  
  sub new {
      my $pkg = shift;
  
      return bless {}, $pkg;
  }
  
  sub print {
      print 'Hello, world!' . "n";
  }
  
  1;