I don’t think that they do. I know that Erlang has something similar; you can reload a module and it will gradually replace the old code as processes are replaced. In principle you could debug a single thread in a C (or C++) program without stopping the others, and some IDEs will let you edit the code and recompile while the program is running (they patch out the old function definition so that it jumps to the new one instead), but good luck doing that in production.
But don’t forget that in Common Lisp, you can redefine classes at run time as well as functions. All existing instances of the class will be updated to the new definition, and you can provide the code that decides how the old fields are translated into the new ones if the default behavior is insufficient. Good luck doing that in C or C++.
My favorite story involved a race condition that was discovered in the code running on a satellite, after it had been launched. The software on the satellite was mostly written in Common Lisp (there was a C component as well), so they opened a connection to the satellite, started the REPL, debugged the problem, and uploaded replacement code (which obviously added a lock or something) to the satellite all through that same REPL. While the satellite was a hundred million miles away from Earth, and while it kept performing it’s other duties. You can’t do that on a system which merely dumps core any time something unexpected happens.
> During that time we were able to debug and fix a race condition that had not shown up during ground testing. (Debugging a program running on a $100M piece of hardware that is 100 million miles away is an interesting experience. Having a read-eval-print loop running on the spacecraft proved invaluable in finding and fixing the problem.
But don’t forget that in Common Lisp, you can redefine classes at run time as well as functions. All existing instances of the class will be updated to the new definition, and you can provide the code that decides how the old fields are translated into the new ones if the default behavior is insufficient. Good luck doing that in C or C++.
My favorite story involved a race condition that was discovered in the code running on a satellite, after it had been launched. The software on the satellite was mostly written in Common Lisp (there was a C component as well), so they opened a connection to the satellite, started the REPL, debugged the problem, and uploaded replacement code (which obviously added a lock or something) to the satellite all through that same REPL. While the satellite was a hundred million miles away from Earth, and while it kept performing it’s other duties. You can’t do that on a system which merely dumps core any time something unexpected happens.