[krastanov]

To elaborate on the sibling comment: Julia has (1) multimethods / multiple dispatch capabilities, (2) you can dynamically define new types and methods at runtime, (3) everything is aggressively devirtualized/compiled to machine code when possible. That requires the capability of discarding and recompiling code that has already been compiled and cached when a new method is defined at runtime. Worse even, just importing a new library might invalidate some of the compiled cached code. For me, capabilities 1,2,and 3 make the cost of a complicated compilation model worth it. But it also means it takes a lot of time to improve the compiler (this type of better caching was not at all a low hanging fruit).