One performance feature I find really nice in Julia, is that you can write your own function (cost function, function to integrate, whatever) that you can pass

One performance feature I find really nice in Julia, is that you can write your own function (cost function, function to integrate, whatever) that you can pass into a solver/integrator/etc. Then it will be inlined and compiled into that external library. Does this work with numba? Are your jit-compiled functions compiled into external modules?