in reply to DWIM: autoloading classes

Does this weird piece of code do what you want? (Needless note to others: Don't use this code. Note to self: Don't write such code!) 
package StupidAutoloader;

use strict;
use warnings;

use Carp;

our %Classes;

sub import {
    my $class = shift;
    my @hierarchies = @_;
    %Classes = map {($_, undef)} @hierarchies;
    *UNIVERSAL::new = sub {
        my $proto = $_[0];
        my $class = ref($proto) || $proto;

        croak "Could not find method new() in package '$class'."
          if ref($proto) or
             exists $INC{$class} or
             not in_hierarchy(\%Classes, $class);
        
        eval "use $class;";
        croak "Error loading module '$class': $@" if $@;
        no strict 'refs';
        goto &{"${class}::new"};
    };
}

sub in_hierarchy {
    my $h = shift;
    my $c = shift;
    return 1 if exists $h->{$c};

    my @levels = split /::/, $c;
    my $accum;
    foreach (@levels) {
        $accum .= $_;
        return 1 if exists $h->{"${accum}::*"}
    }
    return 0;
}

1;

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

use StupidAutoloader 'Data::*';

my $d = Data::Dumper->new([]);
print "$d\n";
my $g = Data::Grouper->new(a => []);
print "$g\n";

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Re: Re: DWIM: autoloading classes
by Ovid (Cardinal) on Sep 17, 2003 at 14:17 UTC

    That's a very interesting piece of code. It never ceases to amaze what sort of things we can do with Perl. The only problem is that not all constructors are named 'new' :)

    Cheers,
    Ovid

    New address of my CGI Course.

[reply]
      That problem is alleviated by fiendishly abusing AUTOLOAD in UNIVERSAL. (There are people who'd kill for this... if you use it in production!) --- 
      #!/usr/bin/perl
use strict;
use warnings;

use StupidAutoloader qw/Math::* Data::*/;

my $function = Math::Symbolic->parse_from_string('1/2*m*v^2');
print $function->simplify(), "\n";

# Doesn't work because Math::Symbolic::Operator *implicitly requires o
+ther
# modules in the Math::Symbolic:: hierarchy:
# my $op = Math::Symbolic::Operator->new(...);

my $cmplx = Math::Complex->new(3, 2);
print $cmplx;

print Data::Dumper->Dump([$function]);

# Even this works:
use StupidAutoloader '*';

my $cgi = CGI->new();
print $cgi->header();

      [download]
      module: 
      package StupidAutoloader;

use strict;
use warnings;

use Carp;

our %Classes;
our $AUTOLOAD;

*UNIVERSAL::AUTOLOAD = sub {
    my $proto = $_[0];
    my $class = ref($proto) || $proto;
    
    my $method_name = $AUTOLOAD;
    die "Could not determine method name."
      if not defined $method_name;
    $method_name =~ /::(\w+)$/ or die;
    $method_name = $1;
    
    croak "Could not find method new() in package '$class'."
      if ref($proto) or
         exists $INC{$class} or
         (not _in_hierarchy(\%Classes, $class) and not exists $Classes
+{'*'});
    
    eval "use $class;";
    croak "Error loading module '$class': $@" if $@;
    no strict 'refs';
    goto &{"${class}::${method_name}"};
};

sub import {
    my $class = shift;
    my @hierarchies = @_;
    foreach (@hierarchies) {
        $Classes{$_} = undef;
    }
}

sub unimport {
    my $class = shift;
    my @hierarchies = @_;
    if (not @hierarchies) {
        %Classes = ();
    }
    foreach (@hierarchies) {
        delete $Classes{$_};
    }
}

sub _in_hierarchy {
    my $h = shift;
    my $c = shift;
    return 1 if exists $h->{$c};

    my @levels = split /::/, $c;
    my $accum;
    foreach (@levels) {
        $accum .= $_;
        return 1 if exists $h->{"${accum}::*"}
    }
    return 0;
}

1;

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