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Comment by shele | Hacker News Reader

On the other hand, Julia can do the right thing dynamically. Your matrix happens to be symmetric? Julia will chose an appropriate factorisation and will propagate that knowledge through dynamic dispatch.

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"Automagical" solutions tend to work until they don't. I would much rather have my solution be provably correct at compilation time than to depend on high-overhead runtime systems.

You don't know what you're talking about.

Tell me where I'm wrong

Julia can and does make 'provably correct' decisions at compile time, it's just that at the the default typesystem settings are not quite correct for machine learning apps.

Also it's not a high overhead runtime. The runtime itself is compiled to highly optimized machine code (it can even compile, say the derivative of f(x) = 5x+3 down to the machine immediate "5" at compile time).

There is a lot of lifting to get that compilation framework into place, so there is a load-time overhead.

You are not wrong. For some "highly dynamic" applications, say, optimizing compiler IR where there are many different subclasses of IR nodes, dynamic dispatch is nice. But when you are running an ML model, scientific application where you already know which sparse matrix format you need, etc, you can do all of that statically with less overhead and performance predictability. This is in no way an argument against Julia; the point is that you don't need dynamic dispatch if you can statically determine what needs to happen.

That is basically the core insight behind julia. The really performance sensitive parts of your application are already static just by the nature of that code, so we can extract that static information to make it really fast. We can also make use of the same static information for static error messages or static compilation and get the best of both world (dynamic during development, static when you're done), but the tooling for that is a bit less developed at the moment.

Which you don't need most of the time in production because you can statically determine which operation needs to happen without the overhead of dynamically choosing the operation.

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