Re: [async-mqtt5] Review questions

From: Vinnie Falco (vinnie.falco_at_[hidden])
Date: 2024-10-20 18:32:20

On Sun, Oct 20, 2024 at 11:13 AM Ivica Siladic via Boost <
boost_at_[hidden]> wrote:

> > What you could do here is to introduce a BOOST_MQTT5_ENABLE_BOOST_LOG
> macro

I don't like configuration macros. Because these create different
libraries, effectively creating separate object files which have the
potential to be incompatible at link-time. It is simpler for there to be
only one version of the library with no configurations.

> our goal is to find a more elegant, C++-style solution that achieves the
> same effect.
>

How do you feel about this?

    template<
        class Stream,
        class Logger = int,
        class TlsContext = std::monostate
    >
    class mqtt_client
    {
        Logger log_; // could use empty base optimization here
    public:
          void cancel() {
            if constexpr(is_logger<Logger>)
                log_("cancelling");
             auto impl = _impl;
            _impl = impl->dup();
            impl->cancel();
        }
        ...

To be honest though, I think you are being unnecessarily strict with the
"zero overhead." There is nothing wrong with adding a single if statement
to each function for logging. Really now, are you worried about the
performance of adding a branch to a function which invokes an initiating
function? I bet if you measure it, you will change your mind.

Thanks