Blog post about my experiences with Julia

[ChrisRackauckas]

@Volker_Weissmann

What would you suggest to debug this code/make the error message nicer?

MethodError: no method matching copyto! · Issue #48 · SciML/SimpleDiffEq.jl · GitHub

@Henrique_Becker

All in all, in fact, I do not find the error message to be bad. It does point to a line of your code, and it is precise about the problem, the issue is that with the broadcasting machinery involved you get names like materialize! and copyto! that mean nothing to the novice programmer. It does not seem to me a problem related to what we were discussing (failing as soon as possible) but the fact that broadcasting error messages are confusing to novices. It would be impossible to fail sooner there because the code takes a generic hook (if I am not wrong), and as so it cannot check the input type against anything. This is a common problem with hooks/callbacks, not a language problem, even if some languages like Haskell were able to do some very aggressive trade-offs that may solve this problem of designing code with hooks/callbacks.

FWIW, I think this is pointing at something I’ve been meaning to open an issue for. Broadcast should really catch errors and throw a higher level error. It really can. Saying “I cannot materialize!” assumes people know some deep stuff. materialize! is not even one of the documented interface functions for Broadcast:

https://docs.julialang.org/en/v1/manual/interfaces/#man-interfaces-broadcasting

So yes, it should catch this and say “In-place Broadcast was not possible with types X, Y, Z.”. And then, even better, if it’s trying to materialize an in-place broadcast to a Number, it should catch that and have an explanation as to why x .= y is never going to work with x = 2.0.

That error message can definitely be better.