Handler Interface Reference

#include <ozo/core/concept.h>

Description

Handler concept.

Handler is a function or a functor which is used as a callback for handling result of asynchronous IO operations in the library.

In case of function it has to have this signature:

template <typename Connection>
void Handler(ozo::error_code ec, Connection&& connection) {
    //...
}

In case of functor it has to have such operator():

struct Handler {
    template <typename Connection>
    void operator() (ozo::error_code ec, Connection&& connection) {
        //...
    }
};

In case of lambda:

auto Handler = [&] (ozo::error_code ec, auto connection) {
    //...
};

Handler has to handle an ozo::error_code object as first argument, and the Connection implementation object as a second one. It is better to define second argument as a template parameter because the implementation depends on a numerous of compile-time options but if it is really needed - real type can be obtained with ozo::connection_type.

Handler has to be invoked according to ec state:

• false — operation succeeded, Connection should be in good state and can be used for an operation.
• true — operation failed and ec contains error, Connection could be in these states:
  • Connection is in null-state — ozo::is_null_recursive() returns true, object is useless;
  • Connection is in bad state — ozo::is_null_recursive() returns false, ozo::connection_bad() returns true or ozo::get_transaction_status() returns not ozo::transaction_status::idle, object may not be used for further operations but it may provide additional error context via ozo::error_message() and ozo::get_error_context() functions.
  • Connection is in good state — ozo::is_null_recursive() returns false, ozo::connection_bad() returns true and ozo::get_transaction_status() returns ozo::transaction_status::idle, object may be used for further operations and may provide additional error context via ozo::error_message() and ozo::get_error_context() functions.