# Optional dependencies and name collisions

**URL:** <https://discourse.julialang.org/t/optional-dependencies-and-name-collisions/15997>\
**Category:** General Usage\
**Tags:** package\
**Created:** [October 7, 2018, 5:47pm UTC](https://discourse.julialang.org/t/optional-dependencies-and-name-collisions/15997 "2018-10-07T17:47:01Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![pablosanjose](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pablosanjose/32/7006_2.png) [@pablosanjose](https://discourse.julialang.org/u/pablosanjose)\
**Post date:** [October 7, 2018, 5:47pm UTC](https://discourse.julialang.org/t/optional-dependencies-and-name-collisions/15997/1 "2018-10-07T17:47:01Z")

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Say I am developing package MyPkg that computes some stuff using an exported type `TA`. The package also contains an optional dependency on Makie, implemented with `Requires.jl`. After my computation using MyPkg, I do `using Makie` to plot the results. The package MyPkg extends the `plot` function from Makie with a method `plot(::TA)`. But since Makie takes a bit to load, Makie is not loaded by MyPkg up front, only when needed (by employing `Requires.jl`).

Here comes the rub. Both package MyPkg and Makie export another function with a common name: `transform!`. The combination of optional dependency and name collision is giving me serious trouble. I do `using MyPkg` and then I can use `transform!(::TA)` defined by MyPkg. But as soon as I do `using Makie` I get

`WARNING: both MyPkg and Makie export "transform!"; uses of it in module Main must be qualified`

From that point on I cannot use `transform!` anymore, just `MyPkg.transform!` and `Makie.transform!`

If the dependency on Makie were not optional I would of course just extend `transform!` from Makie, but with an optional dependency I don’t know how to do that. Any idea?

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**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [October 7, 2018, 5:56pm UTC](https://discourse.julialang.org/t/optional-dependencies-and-name-collisions/15997/2 "2018-10-07T17:56:07Z")

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Use `import` and prefix calls with module name.

Exporting a generic name like `transform!` is really asking for trouble…

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**Author:** ![pablosanjose](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pablosanjose/32/7006_2.png) [@pablosanjose](https://discourse.julialang.org/u/pablosanjose)\
**Post date:** [October 7, 2018, 6:03pm UTC](https://discourse.julialang.org/t/optional-dependencies-and-name-collisions/15997/3 "2018-10-07T18:03:36Z")

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Thanks @kristoffer.carlsson. Renaming `transform!` might end up to be the best solution, but I actually thought it would be possible to merge the `transform!` method tables of both packages, as they act on types defined within the packages themselves (no piracy). Why is it not possible?

To be more specific, this is my use case:

```julia
module MyPkg

using Requires

export transform!, plot, compute

struct TA
    a
end

function compute()
    # ... heady stuff!
    # returns a ::TA
end

function transform!(::TA)
    # ... useful stuff
end

@require Makie = "ee78f7c6-11fb-53f2-987a-cfe4a2b5a57a" begin
    using Makie
    function plot(::TA)
        #plot code
    end
end

end

```

And my usage would be

```julia
using MyPkg
solution = compute() # returns a ::TA
solution2 = transform!(solution)
using Makie # now plot(::TA) is loaded too
plot(solution2)
solution3 = tranform!(solution2) # I cannot do this anymore! I need to say MyPkg.transform!(solution2)

```

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<div class="post-metadata">

**Author:** ![pablosanjose](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pablosanjose/32/7006_2.png) [@pablosanjose](https://discourse.julialang.org/u/pablosanjose)\
**Post date:** [October 7, 2018, 6:11pm UTC](https://discourse.julialang.org/t/optional-dependencies-and-name-collisions/15997/4 "2018-10-07T18:11:10Z")

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I strongly suspect that I am actually doing something wrong here. I actually have the same problem with `plot` as with `transform!`, so this must certainly not be the way to go about this problem of optionally extending functions from other packages… It’s the first time I try.

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<div class="post-metadata">

**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [October 7, 2018, 6:20pm UTC](https://discourse.julialang.org/t/optional-dependencies-and-name-collisions/15997/5 "2018-10-07T18:20:07Z")

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> [@pablosanjose](#):
>
> but I actually thought it would be possible to merge the `transform!` method tables of both packages, as they act on types defined within the packages themselves (no piracy). Why is it not possible?

Automatic method merging would prevent writing generic code since you have no idea anymore what functions mean.

In other words, a generic function is more than just a name. It has a higher-level purpose that can be documented and allow us to write generic code based on that.

By extending a function (e.g `push!`) you are agreeing to the meaning of that function, so in the `push!` case:

```julia
help?> push!

  push!(collection, items...) -> collection

  Insert one or more items at the end of collection.

```

We can now write generic code using `push!` because we know what `push!` does.

It is fine for another function called `push!` to exist which has a completely different meaning, and you chose which one of these you are using based on what you import or by module prefixing.

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<div class="post-metadata">

**Author:** ![pablosanjose](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pablosanjose/32/7006_2.png) [@pablosanjose](https://discourse.julialang.org/u/pablosanjose)\
**Post date:** [October 7, 2018, 6:29pm UTC](https://discourse.julialang.org/t/optional-dependencies-and-name-collisions/15997/6 "2018-10-07T18:29:05Z")

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Aha, that’s a very good point. I’m beginning to get it. For unqualified use of a function one needs to be clear on who is the original owner, and who is extending it. It makes perfect sense. Then, in a case like mine, I have to make sure none of my exported functions are named like any exported functions of an optional dependency. And to extend `plot` I really need to do ~~`using Makie: plot`~~ `import Makie: plot` inside the `@require` so that I acknowledge Makie as the owner.  
Good lesson!

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<div class="post-metadata">

**Author:** ![angusmoore](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/angusmoore/32/5654_2.png) [@angusmoore](https://discourse.julialang.org/u/angusmoore)\
**Post date:** [October 7, 2018, 11:56pm UTC](https://discourse.julialang.org/t/optional-dependencies-and-name-collisions/15997/7 "2018-10-07T23:56:32Z")

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One implication of this genericism is that what a function _means_ needs to be defined somewhere. A common way of organising julia packages is to have a “base” package that defines these function meanings and exports the function names. Specific packages _implement_ those methods for their relevant domain. For instance, StatsBase.jl implements a function called `coeftable`. But the implementation in StatsBase is just an error saying it hasn’t been implemented. The various statistical packages then import that name, implement it as appropriate (e.g. in GLM [lm](https://github.com/JuliaStats/GLM.jl/blob/f3393bfd1101c15584c5cfdb9148295caf1f0a4a/src/lm.jl) for an lm, and [here](https://github.com/JuliaStats/GLM.jl/blob/b5e5cb2c0cb64cb57b7584408706bcd67b40c0b0/src/glmfit.jl) for a glm) and then export it. This way, groups of related packages can coordinate on the meaning of functions, and have a single meta package to import the names from.