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Paul Hoffman > Hash-AsObject-0.13 > Hash::AsObject



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Hash::AsObject - treat hashes as objects, with arbitrary accessors/mutators


    $h = Hash::AsObject->new;
    print $h->foo;       # prints 123
    print $h->{'foo'};   # prints 123
    $h->{'bar'}{'baz'} = 456;
    print $h->bar->baz;  # prints 456


A Hash::AsObject is a blessed hash that provides read-write access to its elements using accessors. (Actually, they're both accessors and mutators.)

It's designed to act as much like a plain hash as possible; this means, for example, that you can use methods like DESTROY to get or set hash elements with that name. See below for more information.


The whole point of this module is to provide arbitrary methods. For the most part, these are defined at runtime by a specially written AUTOLOAD function.

In order to behave properly in all cases, however, a number of special methods and functions must be supported. Some of these are defined while others are simply emulated in AUTOLOAD.

    $h = Hash::AsObject->new;
    $h = Hash::AsObject->new(\%some_hash);
    $h = Hash::AsObject->new(%some_other_hash);

Create a new Hash::AsObject.

If called as an instance method, this accesses a hash element 'new':

    $h->{'new'} = 123;
    $h->new;       # 123
    $h->new(456);  # 456

This method cannot be used to access a hash element 'isa', because Hash::AsObject doesn't attempt to handle it specially.


Similarly, this can't be used to access a hash element 'can'.

    $h->{'AUTOLOAD'} = 'abc';
    $h->AUTOLOAD;       # 'abc'
    $h->AUTOLOAD('xyz') # 'xyz'

Hash::AsObject::AUTOLOAD recognizes when AUTOLOAD is begin called as an instance method, and treats this as an attempt to get or set the 'AUTOLOAD' hash element.

    $h->{'DESTROY'} = [];
    $h->DESTROY;    # []
    $h->DESTROY({}) # {}

DESTROY is called automatically by the Perl runtime when an object goes out of scope. A Hash::AsObject can't distinguish this from a call to access the element $h->{'DESTROY'}, and so it blithely gets (or sets) the hash's 'DESTROY' element; this isn't a problem, since the Perl interpreter discards any value that DESTROY returns when called automatically.


When called as a class method, this returns $Hash::AsObject::VERSION; when called as an instance method, it gets or sets the hash element 'VERSION';


Since Hash::AsObject doesn't export any symbols, this method has no special significance and you can safely call it as a method to get or set an 'import' element.

When called as a class method, nothing happens.

The methods can() and isa() are special, because they're defined in the UNIVERSAL class that all packages automatically inherit from. Unfortunately, this means that you can't use Hash::AsObject to access elements 'can' and 'isa'.


No distinction is made between non-existent elements and those that are present but undefined. Furthermore, there's no way to delete an element without resorting to delete $h->{'foo'}.

Storing a hash directly into an element of a Hash::AsObject instance has the effect of blessing that hash into Hash::AsObject.

For example, the following code:

    my $h = Hash::AsObject->new;
    my $foo = { 'bar' => 1, 'baz' => 2 };
    print ref($foo), "\n";
    print ref($foo), "\n";

Produces the following output:


I could fix this, but then code like the following would throw an exception, because $h->foo($foo) will return a plain hash reference, not an object:


Well, I can make $h->foo($foo)->bar work, but then code like this won't have the desired effect:

    my $foo = { 'bar' => 123 };
    print $foo->{'bar'};  # prints 123
    print $h->foo->bar;   # prints 456

I suppose I could fix that, but that's an awful lot of work for little apparent benefit.

Let me know if you have any thoughts on this.


Autovivification is probably not emulated correctly.

The blessing of hashes stored in a Hash::AsObject might be considered a bug. Or a feature; it depends on your point of view.





Paul Hoffman <nkuitse AT cpan DOT org>


Andy Wardley for Template::Stash, which was my inspiration. Writing template code like this:

    [% %]

Made me yearn to write Perl code like this:



Copyright 2003-2007 Paul M. Hoffman. All rights reserved.

This program is free software; you can redistribute it and modify it under the same terms as Perl itself.

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