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use Tie::Constrained;

tie my $array_ref,
    'Tie::Constrained', sub { ref $_[0] eq 'ARRAY' };

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tie my $hash_ref,
    'Tie::Constrained', sub { ref $_[0] eq 'HASH' };
...
    'Tie::Constrained',
    sub { ref $_[0] and $_[0]->isa('CGI') },
    CGI->new;