# IndirectArray indexing

**URL:** <https://discourse.julialang.org/t/indirectarray-indexing/135974>\
**Category:** General Usage\
**Tags:** question\
**Created:** [March 2, 2026, 11:14pm UTC](https://discourse.julialang.org/t/indirectarray-indexing/135974 "2026-03-02T23:14:16Z")\
**Posts on this page:** 11\
**Page:** 1

<div class="post-metadata">

**Author:** ![magister-ludi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/magister-ludi/32/4003_2.png) [@magister-ludi](https://discourse.julialang.org/u/magister-ludi)\
**Post date:** [March 2, 2026, 11:14pm UTC](https://discourse.julialang.org/t/indirectarray-indexing/135974/1 "2026-03-02T23:14:16Z")

</div>

I have a PNG file that loads as an `IndirectArray` with an `eltype` of `RGB{N0f8}`:  
 ![mwe](https://global.discourse-cdn.com/julialang/original/3X/c/e/ce7076f940a9391cbf3f8cf0f13b0790781cb7b4.png)  
I use the following code:

```julia-auto
using FileIO
using ImageIO

function f()
    img = load("mwe.png")
    @show typeof(img)
    return img[1]
end

```

Calling `f()` gives the following result:

```julia-auto
typeof(img) = IndirectArrays.IndirectArray{ColorTypes.RGB{FixedPointNumbers.N0f8}, 2, UInt8, Matrix{UInt8}, OffsetArrays.OffsetVector{ColorTypes.RGB{FixedPointNumbers.N0f8}, Vector{ColorTypes.RGB{FixedPointNumbers.N0f8}}}}
CanonicalIndexError: getindex not defined for OffsetArrays.OffsetVector{ColorTypes.RGB{FixedPointNumbers.N0f8}, Vector{ColorTypes.RGB{FixedPointNumbers.N0f8}}}
Stacktrace:
 [1] error_if_canonical_getindex(::IndexCartesian, A::OffsetArrays.OffsetVector{ColorTypes.RGB{FixedPointNumbers.N0f8}, Vector{ColorTypes.RGB{FixedPointNumbers.N0f8}}}, ::Int64)
   @ Base .\abstractarray.jl:1357
 [2] getindex
   @ .\abstractarray.jl:1341 [inlined]
 [3] _getindex
   @ .\abstractarray.jl:1388 [inlined]
 [4] getindex
   @ .\abstractarray.jl:1342 [inlined]
 [5] getindex(A::IndirectArrays.IndirectArray{ColorTypes.RGB{FixedPointNumbers.N0f8}, 2, UInt8, Matrix{UInt8}, OffsetArrays.OffsetVector{ColorTypes.RGB{FixedPointNumbers.N0f8}, Vector{ColorTypes.RGB{FixedPointNumbers.N0f8}}}}, i::Int64)
   @ IndirectArrays ...\.julia\packages\IndirectArrays\BUQO3\src\IndirectArrays.jl:64
 [6] f()
   @ Main .\REPL[2]:4
 [7] top-level scope
   @ REPL[3]:1

```

A second call of the function gives the result I expected on the first call:

```julia-auto
typeof(img) = IndirectArrays.IndirectArray{ColorTypes.RGB{FixedPointNumbers.N0f8}, 2, UInt8, Matrix{UInt8}, OffsetArrays.OffsetVector{ColorTypes.RGB{FixedPointNumbers.N0f8}, Vector{ColorTypes.RGB{FixedPointNumbers.N0f8}}}}
RGB{N0f8}(1.0, 1.0, 1.0)

```

Is there something I should be doing before the first `getindex` operation to ensure that it works?

---

<div class="post-metadata">

**Author:** ![tim.holy](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tim.holy/32/52_2.png) [@tim.holy](https://discourse.julialang.org/u/tim.holy)\
**Post date:** [March 2, 2026, 11:16pm UTC](https://discourse.julialang.org/t/indirectarray-indexing/135974/2 "2026-03-02T23:16:31Z")

</div>

It’s surely a world-age error. Try `using IndirectArrays` at the top of your file.

---

<div class="post-metadata">

**Author:** ![magister-ludi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/magister-ludi/32/4003_2.png) [@magister-ludi](https://discourse.julialang.org/u/magister-ludi)\
**Post date:** [March 2, 2026, 11:27pm UTC](https://discourse.julialang.org/t/indirectarray-indexing/135974/3 "2026-03-02T23:27:14Z")

</div>

Thanks for the quick reply. Unfortunately, I get the same result.

---

<div class="post-metadata">

**Author:** ![Benny](https://avatars.discourse-cdn.com/v4/letter/b/49beb7/32.png) [@Benny](https://discourse.julialang.org/u/Benny)\
**Post date:** [March 3, 2026, 12:27am UTC](https://discourse.julialang.org/t/indirectarray-indexing/135974/4 "2026-03-03T00:27:59Z")

</div>

Odd, I don’t get the error or the IndirectArray (Windows, Julia v1.12.5, FileIO v1.18.0, ImageIO v0.6.9, IndirectArrays v1.0.0):

```julia-auto
julia> f()
typeof(img) = Matrix{ColorTypes.RGB{FixedPointNumbers.N0f8}}
RGB{N0f8}(1.0, 1.0, 1.0)

```

I right-click-saved the PNG image, maybe something was lost there?

> [@magister-ludi](#):
>
> Is there something I should be doing before the first `getindex` operation to ensure that it works?

That’s a package’s job, it’s abnormal for a first call to define a needed method.

---

<div class="post-metadata">

**Author:** ![magister-ludi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/magister-ludi/32/4003_2.png) [@magister-ludi](https://discourse.julialang.org/u/magister-ludi)\
**Post date:** [March 3, 2026, 1:08am UTC](https://discourse.julialang.org/t/indirectarray-indexing/135974/5 "2026-03-03T01:08:00Z")

</div>

I think the discourse software (or the browser) converts the format. I have put a copy of the original file [here](https://github.com/magister-ludi/mwe.git).

> That’s a package’s job, it’s abnormal for a first call to define a needed method.

The package defines `getindex(A::IndirectArray, i::Int)`, in a way that looks perfectly reasonable, but the error is thrown once control gets to `Base`.

---

<div class="post-metadata">

**Author:** ![Benny](https://avatars.discourse-cdn.com/v4/letter/b/49beb7/32.png) [@Benny](https://discourse.julialang.org/u/Benny)\
**Post date:** [March 3, 2026, 3:38am UTC](https://discourse.julialang.org/t/indirectarray-indexing/135974/6 "2026-03-03T03:38:38Z")

</div>

I’m seeing the same error and array types now. Seeing something else weird:

```julia-auto
julia> load("mwe.png") |> typeof
IndirectArrays.IndirectArray{ColorTypes.RGB{FixedPointNumbers.N0f8}, 2, UInt8, Matrix{UInt8}, OffsetArrays.OffsetVector{ColorTypes.RGB{FixedPointNumbers.N0f8}, Vector{ColorTypes.RGB{FixedPointNumbers.N0f8}}}}

julia> load("mwe.png") |> IndexStyle
IndexLinear()

julia> load("mwe.png").values |> typeof
OffsetVector{RGB{N0f8}, Vector{RGB{N0f8}}} (alias for OffsetArrays.OffsetArray{ColorTypes.RGB{FixedPointNumbers.Normed{UInt8, 8}}, 1, Array{ColorTypes.RGB{FixedPointNumbers.Normed{UInt8, 8}}, 1}})

julia> load("mwe.png").values |> IndexStyle
IndexLinear()

```

So where did that `IndexCartesian` come from? The last `getindex` just calls `IndexStyle` like the above:

```julia-auto
function getindex(A::AbstractArray, I...)
    @_propagate_inbounds_meta
    error_if_canonical_getindex(IndexStyle(A), A, I...) # L1341
    _getindex(IndexStyle(A), A, to_indices(A, I)...)
end

```

---

<div class="post-metadata">

**Author:** ![magister-ludi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/magister-ludi/32/4003_2.png) [@magister-ludi](https://discourse.julialang.org/u/magister-ludi)\
**Post date:** [March 3, 2026, 5:43am UTC](https://discourse.julialang.org/t/indirectarray-indexing/135974/7 "2026-03-03T05:43:30Z")

</div>

…and why does it suddenly work after the first call to `getindex`?

---

<div class="post-metadata">

**Author:** ![tim.holy](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tim.holy/32/52_2.png) [@tim.holy](https://discourse.julialang.org/u/tim.holy)\
**Post date:** [March 3, 2026, 7:49am UTC](https://discourse.julialang.org/t/indirectarray-indexing/135974/8 "2026-03-03T07:49:32Z")

</div>

Still a world age error. But the missing packages turned out to be `OffsetArrays` and `ColorVectorSpace`.

The issue is that `load` loads packages on-demand, but this means new methods are getting defined while your _compiled_ function `f` is running. Those are defined in a new world, but the compiled function is running in the old world. When you come back to the command-line prompt, the world age updates, so the next run works as expected.

Here’s how to diagnose what’s missing:

```julia-auto
julia> using FileIO, ImageIO

julia> function f()
           img = load("mwe.png")
               @show typeof(img)
           return img[1]
       end
f (generic function with 1 method)

julia> mods = Base.loaded_modules_array();

julia> f()
typeof(img) = IndirectArrays.IndirectArray{ColorTypes.RGB{FixedPointNumbers.N0f8}, 2, UInt8, Matrix{UInt8}, OffsetArrays.OffsetVector{ColorTypes.RGB{FixedPointNumbers.N0f8}, Vector{ColorTypes.RGB{FixedPointNumbers.N0f8}}}}
ERROR: CanonicalIndexError: getindex not defined for OffsetArrays.OffsetVector{ColorTypes.RGB{FixedPointNumbers.N0f8}, Vector{ColorTypes.RGB{FixedPointNumbers.N0f8}}}
Stacktrace:
 [1] error_if_canonical_getindex(::IndexCartesian, A::OffsetArrays.OffsetVector{ColorTypes.RGB{FixedPointNumbers.N0f8}, Vector{ColorTypes.RGB{FixedPointNumbers.N0f8}}}, ::Int64)
   @ Base .\abstractarray.jl:1357
 [2] getindex
   @ .\abstractarray.jl:1341 [inlined]
 [3] _getindex
   @ .\abstractarray.jl:1388 [inlined]
 [4] getindex
   @ .\abstractarray.jl:1342 [inlined]
 [5] getindex(A::IndirectArrays.IndirectArray{ColorTypes.RGB{FixedPointNumbers.N0f8}, 2, UInt8, Matrix{UInt8}, OffsetArrays.OffsetVector{ColorTypes.RGB{FixedPointNumbers.N0f8}, Vector{ColorTypes.RGB{FixedPointNumbers.N0f8}}}}, i::Int64)
   @ IndirectArrays C:\Users\timho\.julia\packages\IndirectArrays\BUQO3\src\IndirectArrays.jl:64
 [6] f()
   @ Main .\REPL[4]:4
 [7] top-level scope
   @ REPL[6]:1

julia> mods2 = Base.loaded_modules_array();

julia> setdiff(mods2, mods)
20-element Vector{Module}:
 Reexport
 Statistics
 FixedPointNumbers
 ColorTypes
 Colors
 TensorCore
 ColorVectorSpace
 OffsetArrays
 PaddedViews
 MappedArrays
 StackViews
 MosaicViews
 Preferences
 PrecompileTools
 ImageCore
 JLLWrappers
 libpng_jll
 CEnum
 PNGFiles
 StyledStringsExt

```

But if you make sure that all the methods are defined before you run `f` for the first time (by pre-loading the required packages), then it works on first call.

`load` is convenient, but also a foot-gun for this reason.

---

<div class="post-metadata">

**Author:** ![magister-ludi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/magister-ludi/32/4003_2.png) [@magister-ludi](https://discourse.julialang.org/u/magister-ludi)\
**Post date:** [March 3, 2026, 10:47am UTC](https://discourse.julialang.org/t/indirectarray-indexing/135974/9 "2026-03-03T10:47:53Z")

</div>

> [@tim.holy](#):
>
> OffsetArrays

Thanks again for looking at this (thanks also to @Benny). The minimum that will work in this case is

```julia-auto
using FileIO, ImageIO, OffsetArrays

```

I will look into pre-load options. Is there an alternative to `load`? I would rather abandon convenience for reliability.

---

<div class="post-metadata">

**Author:** ![tim.holy](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tim.holy/32/52_2.png) [@tim.holy](https://discourse.julialang.org/u/tim.holy)\
**Post date:** [March 3, 2026, 1:07pm UTC](https://discourse.julialang.org/t/indirectarray-indexing/135974/10 "2026-03-03T13:07:35Z")

</div>

One option might be to add a `noimports=true` kwarg to load, and have it throw an error when it needs to load a package in order to satisfy the request. If you don’t want to implement that yourself, I would guess making that kind of change should be well within the capabilities of modern AI agents, so either way I encourage you to give it a try and submit a PR if it works.

---

<div class="post-metadata">

**Author:** ![magister-ludi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/magister-ludi/32/4003_2.png) [@magister-ludi](https://discourse.julialang.org/u/magister-ludi)\
**Post date:** [March 3, 2026, 10:53pm UTC](https://discourse.julialang.org/t/indirectarray-indexing/135974/11 "2026-03-03T22:53:59Z")

</div>

Thanks for the feedback. I’ll take a look and see whether I can produce something that seems usable.