use Exporter::Tidy default => [ qw(transaction select_handle commit ro
+llback) ];

sub select_handle {
    require Carp;
    Carp::croak("Can't select handle outside transaction");
}

sub _cant_change {
    require Carp;
    Carp::croak("Can't change handle during transaction");
}

sub transaction (&) {
    my ($block) = @_;
    my ($caller, $handle);

    my $caller = caller();

    local *{"${caller}::select_handle"} = sub {
        $handle = shift;
        *{"${caller}::select_handle"} = \&_cant_change;
    };

    # ...
}
[download]

transaction {
    select_handle($dhb);
    # ...
};
[download]

Makeshifts last the longest.

transaction { select_handle($dhb); ... };

Not an option, because you need the handle before you begin the transaction. Won't begin the transaction inside the block, because that would allow stuff to be done outside the transaction while visually, it's in the transaction code block.

Simple to use modules have their limitations. The limitation of this one is that you shouldn't use nested transactions. I think that's acceptable in most cases.

I've only seen nested transactions being used to rollback multiple things. But it's easy to create a wrapper module for that:

package NeedsAName;

sub new { return bless \@_, shift }
sub AUTOLOAD { $_->$AUTOLOAD(@_) for @{+shift}; }

package main;

use Transactions;

my $dbh1 = DBI->connect(...);
my $dbh2 = DBI->connect(...);

our $T = NeedsAName->new($dbh1, $dbh2);

transaction {
    ...
};
[download]

Juerd # { site => 'juerd.nl', plp_site => 'plp.juerd.nl', do_not_use => 'spamtrap' }

Won't begin the transaction inside the block, because that would allow stuff to be done outside the transaction while visually, it's in the transaction code block.

By the same token you can calculate the question to 42 after you finish working with the handle but before you leave the transaction block. You're simply going to have to rely on discipline on that one. Perl always does so a bit more than other languages anyway.

Makeshifts last the longest.