#include <x/sentry.H> void transaction(const DBH &dbh) { auto transaction_sentry=x::make_sentry( [&] { dbh->rollback(); } ); dbh->begin(); transaction_sentry.guard(); // ... dbh->commit(); transaction_sentry.unguard(); }
x::make_sentry
implements an ad-hoc RAII design pattern using a lambda.
x::make_sentry() returns an object that should
exist on the stack.
If the object goes out of scope after
guard() and before
unguard(), the object's destructor invokes the
lambda.
In the example above, an exception that gets thrown any time after the
begin(), and before the
commit(), results in the
rollback() getting automatically invoked.
The lambda should not throw exceptions,
although a thrown
x::exception
is going to get caught, and logged.