Closed sinkers0s closed 1 year ago
Have a look at HOWTO Fix Multiple Definitions Linker Error or do some more research how to use h-only libraries, with the pros and cons.
Search for the reasons in many discussions / issues in many other libraries, and how other people can currently use them.
Describe the bug
The reason for we can only include
AsyncMqtt_Generic.h
in one .cpp or .ino is because it contains not only headers but also implementations. In particular,AsyncMqtt_Generic.h
:Which
AsyncMqttClient_Generic_Impl.h
is actually implementation instead of header. In common practice, theAsyncMqttClient_Generic_Impl.h
should end with .cpp/.c instead of .h. And use compiler configuration/compile script to let compiler compile it as object(and later linking) explicitly. I'm curious why you take this approach to put header and implementation together. Is that something I missed?And here's a problem: this approach makes abstracting/inheriting or even simply include in multiple files within same project impossible without modifying your code. For example: 1) include
AsyncMqtt_Generic.h
in two cpp(ino is actually cpp) of same project will result double definition. 2) include onlyAsyncMqttClient_Generic.hpp
will result implementation not found, even if I use some trick to let compiler compile theAsyncMqttClient_Generic_Impl.h
. I can do this inAsyncMqttClient_Generic_Impl.h
for latter to make things work:But then I have to modify your code. It's not "generic" anymore. So may I ask why would you take this approach?