I can can create a zero dimensional array of Nothing: julia> Array{Nothing, 0}(nothing) 0-dimensional Array{Nothing, 0}: nothing but not other types: julia> Array{String, 0}("") ERROR: MethodError: no method matching Array{String, 0}(::String) julia> Array{Tuple{Nothing}, 0}((nothing,)) ERROR: M…

The issue here is that this method isn’t for initializing an array with values. It’s only for initializing an array with an “initializer” object, which can be one of undef, nothing or missing, telling Array how to initialize the array initially. This is documented in the docstring of the Array const…

Why do these special cases missing/nothing exist? Array{Union{Float32,Missing}}(missing, 1,3) is (roughly?) a special syntax for fill!(Array{Union{Float32,Missing}}(undef, 1,3), missing), but the docs don’t really offer a reason to treat these two specially. Is there some optimsation these allow? T…

I see, so this is nothing specific to zero-dimensional arrays. It’s true for Arrays generally. I saw a discussion elsewhere too, but this means that if you want to initialize an array that takes, say Int64, you’ll need to actually create an array that accepts Union{Nothing, Int64}. Seems clunky and…

[image] sadish-d: but this means that if you want to initialize an array that takes, say Int64, you’ll need to actually create an array that accepts Union{Nothing, Int64}. No, you don’t. You can write fill(1, 2, 3) or fill!(Array{Int}(undef, 2, 3), 1). These are the same for all types. The n…

@mcabbott I should have said “to initialize a placeholder array that later takes Int64”. I understand that fill works if you already know what you want to put in the array.

[image] sadish-d: “to initialize a placeholder array that later takes Int64”. I think this is usually called an uninitialised array – you create the array, but don’t initialise its values. This is what undef is for. (And similar.) You should not touch missing/nothing unless you have reason to…

I guess it makes sense that it’s called “uninitialized”. I am not familiar with computer science terminology. But thanks for the note on undef.

Here is a long discussion on how #undef came about.

Zero-dimensional arrays are acting strange

New to Julia

sadish-d March 31, 2023, 8:52pm 9

For anyone interested, here’s some earlier discussion on a similar topic. People smarter than I also tend to think that behavior of Array{Int64, 1}(), Array{Int64, 0}(), Array{Int64, 2}() is inconsistent.

Topic		Replies	Views
Why does Array{Int}() product Array{Int, 0} and not Array{Int, 1} New to Julia	32	1841	June 5, 2018
Handy function for making empty arrays Internals & Design	5	777	February 29, 2020
When I declare an empty array, what does the output given by the typeof method mean? New to Julia	17	5102	May 3, 2021
Irregularity in array definition API General Usage	4	372	July 23, 2020
Why Have 0-Dimensional Arrays? General Usage question	6	8847	December 8, 2016

Zero-dimensional arrays are acting strange

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