[socialdemocrat]

The combination. E.g multiple dispatch without JIT would be really slow as you are picking a method to run at runtime based on the type of all the function arguments.

That requires a linear search through a list of all possible combinations of input arguments.

In a single dispatch language like most object oriented languages, you can do a simple dictionary/hash table lookup. Much faster.

With the JIT Julia is able the optimize away most of these super slow lookups at runtime. Hence you get multiple dispatch for all functions but with fantastic performance. Nobody had done that before.

[mbauman]

FWIW, Julia does segment its method tables into multiple layers depending upon size and type. Multiple dispatch is a strict superset of single-dispatch, and indeed the first layer is just a dictionary/hash table lookup on the first argument. If there's only one result there, you're done (and have the same ~cost for the same ~complexity).

[socialdemocrat]

Thanks, I didn't know that! Has it always been like that? I wondering where I got the idea that it was always a linear search from? Maybe that is just the conceptual way of explaining it.