[gleenn]

Clojure absolutely does not reflect on every call, and no it does require type hinting every argument to every function to get that speed. Especially after Clojure 1.8 came out, huge performance gains were had by inlining far more direct function calls. You can achieve near Java performance on most code, especially if you are okay sacrificing the immutable data structures and lazy sequences. I think this is what makes Clojure shine: you get a beautiful, functional, immutable, easy to understand world, and mostly it is extremely performant, and if it's not, you can have a few functions wrapping uglier but more performant bits, and Java interop is also extremely easy if you want to drop another level down. All the Java tooling for analyzing stack traces and bottlenecks works pretty well if you need to chase performance issues too. And my god it's going to be a lot faster than a lot of Ruby and Python etc apps. I say that with love as long term Rails programmer.

[thom]

You do still need to use type hints to achieve best performance, especially in numerical code. That said, even if I’m doing primitive math and using arrays in Clojure for performance sensitive code, it’s still a nicer experience than other JVM languages for me.