Unless you absolutely positively want exactly that internal data structure, you can solve the general problem with speed and elegance by using one of the Class::Accessor modules.

That gives you a mature, extensible and (in my opinion) well-designed solution to the problem and others like it in your codebase.

Of course, it's possible that this isn't dynamic enough for you, and that you already know Class::Accessor like the back of your hand and the CTO insists that the API is frozen and so on. But if not, I'd really recommend you use Class::Accessor (or Class::Accessor::Fast or Class::Accessor::Faster). I bet you could make a factory on top of that if you really need one.

Anyhow, here's a simple example of that module in action:

package Foo;

use strict;
use warnings;

use base qw(Class::Accessor);
__PACKAGE__->mk_accessors(qw(spiro london));

1;
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Meanwhile, in a nearby t/*.t:

my $foo = Foo->new( { spiro => 'Agnew', london => 'England' } );
isa_ok( $foo, 'Foo' );
is( $foo->spiro,  'Agnew',   "spiro" );
is( $foo->london, 'England', "london" );
ok( $foo->spiro('Not really Agnew'), "set spiro" );
ok( $foo->london('Ontario'),         "set london" );
is( $foo->spiro,  'Not really Agnew', "spiro" );
is( $foo->london, 'Ontario',          "london" );
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