Move definition logger to cpp to avoid "multiple definition" linker error

[tpoignonec]

Hi!

I ran into a little linking issue caused by the kinematics_interface package, more precisely by the definition of rclcpp::Logger LOGGER in kinematics_interface.hpp.

This repos contains the minimal example to reproduce the error, but in a nutshell:

• Header class_a.hpp of ClassA includes kinematics_interface/kinematics_interface.hpp;
• Header class_b.hpp of ClassB includes class_a.hpp

This setups leads to multiple definitions of rclcpp::Logger LOGGER and ultimatly to a linker error:

/usr/bin/ld: CMakeFiles/test_kinematics_interface.dir/src/class_b.cpp.o:(.bss+0x0): multiple definition of `kinematics_interface::LOGGER'; CMakeFiles/test_kinematics_interface.dir/src/class_a.cpp.o:(.bss+0x0): first defined here
collect2: error: ld returned 1 exit status

To avoid this, could you split the code between header and cpp as proposed in the PR?

Note that in there, the rclcpp::Logger is declared as extern, but I guess the declaration of the logger in the header could actually be removed if not used by inherited interfaces (e.g., the KDL one redefine its own).
Alternatively, if it really has to be a header-only package, maybe the variable could just be removed or hidden in a get_logger() function.

What do you think?

Thanks!

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[destogl]

This looks reasonable to me.

[christophfroehlich]

@Mergifyio backport humble

[mergify]

backport humble

✅ Backports have been created

• #32 Move definition logger to cpp to avoid "multiple definition" linker error (backport #21) has been created for branch humble