As subject says, instead of isempty(nothing) ERROR: MethodError: no method matching start(::Void)

nothing is not a container or an iterable, it is a value. While some languages conflate these things, Julia distinguishes the empty tuple (), the boolean false, and special values like nothing (which, are in fact, nothing special, just some conventions make them seem so, cf Missings.missing).

[image] joa-quim: hordes of new users that Julia is expecting to attract from other languages I don’t know what “Julia” is expecting. Personally, I hope that newcomers recognize the fact that languages are different, and when learning a new language, it is inevitable that some initial assump…

[image] Tamas_Papp: eg an error indicating that the question does not make sense. Sorry wanting to know if a variable contains something or not does make a lot of sense me. Period, no more technical details. Is it empty or not? I do have a solution for this but it’s my firm believe that Juli…

Why does it make sense to ask if nothing is empty?

Personally, I find the “box” mental model for variables to be wholly confusing and not helpful — especially for newcomers to the language. Julia’s variables don’t really “contain” values. They’re just names. That’s it.

For example because findfirst may return a nothing and I find the most reasonable to ask isempty(findfirst(...))

Why wouldn’t you write findfirst(...) == nothing?

And why wouldn’t isempty(nothing) give the obvious answer, which is true?

If you want to know if a value is nothing the obvious way to ask that is to check if it’s equal to nothing. How is asking if it’s empty obvious? It seems equally possible that nothing would be a 1-element container containing only itself, which means that it’s not empty.

One thing that could maybe be useful is some sort of trait that would tell whether I’m allowed to call isempty on a given type: say a function iscontainer that would specify whether the argument is a container and so if I can try checking if it has elements. Does something like that exist? It would …

Shouldn't isempty(nothing) return true?

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Shouldn't isempty(nothing) return true?

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