I’m trying to figure out a functionality of Makie.jl, which I can’t find in documentation. In the process, I noticed a syntax I don’t understand: julia> s = Scene() julia> fieldnames(Scene) (:parent, :events, :px_area, :clear, :camera, :camera_controls, :data_limits, :transformation, :plots, :them…

Is update_limits a Ref? julia> x = Ref{Int}() Base.RefValue{Int64}(0) julia> x[] = 1 1 julia> x Base.RefValue{Int64}(1) julia> x[] 1

getindex without the indices is the generic syntax to access the only element of a single-element container, a Ref but also a plain Array: julia> x = [1] 1-element Array{Int64,1}: 1 julia> x[] 1 julia> getindex(x) 1

[image] johnmyleswhite: Is update_limits a Ref ? I don’t know: julia> typeof(s.update_limits) Observable{Any} Thank you for pointing me towards references. The search engine for Julia manual is helpless with "[]" or [] search queries. I get zero or 152 unrelated results.

[image] pauljurczak: julia> typeof(s.update_limits) Observable{Any} I assume this is from Observables.jl ? If so, quoting from the documentation :

Nice @giordano , learned something new today :slight_smile: Is it correct to say that a[] is also better than a[1] because it is converted to a[begin]? So it uses the correct firstindex for the collection?

I wouldn’t encourage using a[] for arrays, a[begin] is more explicit and clear, albeit a bit verbose (and I think requires Julia v1.something, with something != 0). But for single-element arrays maybe it’s fine anyway :thinking: Edit: the problem of [] is that it breaks with containers with more t…

How does s = S() s.aname[] work when aname is not a field name of type S?

I didn’t want to imply that’s a bug, only point out that if you expect to work with any container (of any size!) you can have problems :slightly_smiling_face:

[image] mbauman: It’s wholly consistent with how omitting indexing dimensions work in general It would help if this statement in the manual: When omitting all indices with A[], this semantic provides a simple idiom to retrieve the only element in an array and simultaneously ensure that ther…

What does [] mean in this case?

General Usage

mbauman July 16, 2020, 1:34pm 9

That’s a feature! It’s wholly consistent with how omitting indexing dimensions work in general. In other words, it’s a nice shorthand for grabbing the only element — and ensuring that there’s only one.

Topic		Replies	Views
What is empty index notation? General Usage question , makie	8	683	April 20, 2022
Recovering MATLAB addict needs help to understand Julia indexing General Usage makie	1	396	February 25, 2021
Juliacall access zero-dimensional array with [] New to Julia juliacall	3	377	June 22, 2023
Zero-dimensional array interface for custom type General Usage	1	202	February 23, 2024
Why does `[42][]` work? General Usage indexing , arrays	6	915	January 17, 2019

What does [] mean in this case?

Related topics