I heard a rumour that Julia’s multiple dispatch is “fake news”, in reality it’s overloading because you compile the function before it is run and all you are doing in Julia is just a series of compile and run actions. Is this true? Thanks in advance.

I apologize ahead of time for resurrecting an old thread here, but I think a brief summary of this discussion might be helpful for posterity. There is a lot of confusion in this thread over semantics and definitions, which likely makes it rather time consuming and difficult to read for newcomers and…

Also I would say for myself, if I was just learning it, I would know that I do not yet have a feel of things and knowing two features are useful should be enough to know that the combination of them is useful in general. The counterexample to this is something that needs more explaination (i.e. why …

[image] ffevotte: Exactly, and I guess this is my point: I’m always struggling to come up with real-life examples that are: convincing enough for seasoned developers to understand the interest of multiple dynamic dispatch (as opposed to single dynamic dispatch that they might have in their fav…

As a side note, I find this thread super helpful in understanding how Julia’s semantics compare with languages like C++.

Mee too. I must say I also had the same questions as the OP back when I was learning Julia. I honestly hope @dataSurfer didn’t get the impression that the community didn’t appreciate this thread and his/her contending replies (and that of all other experts involved here of course). They were quite i…

[image] Tamas_Papp: Multiple dispatch is one of those things that you don’t realize you need until you are using it, and then you wonder how you could ever program without again. Julia’s parametric multiple dispatch is a game changer in the same way CLOS was. However, if you are out to convince …

[image] ffevotte: the magic about Julia is the compiler’s ability to generate optimized code for all specialized versions of a method. This happens all the time, is key in how Julia operates and achieves performance, and I don’t have much difficulty explaining the benefit of this. I am probab…

The key is that by compiling methods for specific types, you avoid far more type-checks than you add. This is because if you have a function and the input types of the arguments, you can figure out the types of all variables used in the function (yes there are some exceptions). The result of this is…

Are you are basically agree that runtime type check make performance worse but arguing that Julia compiler is trying hard (and is good) to avoid dynamic dispatch? Because it is (“for almost all functions, the compiler never has to perform type-checks”) useless for almost all cases?

That’s more or less correct but the compiler isn’t trying very hard. The approach julia take is to specialize on the argument type in the compiler, and then teach the users to exploid it for peerformance so it’s not just the job of the compiler if you are trying to compare it with a different langua…

The way I see it, in an expressive language some type checks are inevitable. This is because if you don’t want to write the same code over and over, you need functions that can accept a variety of types as input. This means you (semantically compilers in some but not all cases can solve this) eithe…

Claim (false): Julia isn't multiple dispatch but overloading

General Usage

Liso July 7, 2020, 5:13pm 96

I am probably missing something. How could permanent runtime type check (and runtime method selection) help to achieve better performance?

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Claim (false): Julia isn't multiple dispatch but overloading

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