SYNOPSIS

    my $change = Monorail::Change::AlterField->new(
        table => $from->table->name,
        from  => {
            name           => $from->name,
            type           => $from->data_type,
            is_nullable    => $from->is_nullable,
            is_primary_key => $from->is_primary_key,
            is_unique      => $from->is_unique,
            default_value  => $from->default_value,
            size           => $from->size,
        },
        to => {
            name           => $to->name,
            type           => $to->data_type,
            is_nullable    => $to->is_nullable,
            is_primary_key => $to->is_primary_key,
            is_unique      => $to->is_unique,
            default_value  => $to->default_value,
            size           => $to->size,
        }
    );

    if ($change->has_changes) {
        return $change->as_perl
    }
    else {
        return;
    }