# Proposal for SharedFunctions.jl package for optional dependency management

**URL:** <https://discourse.julialang.org/t/proposal-for-sharedfunctions-jl-package-for-optional-dependency-management/23526>\
**Category:** Internals & Design\
**Created:** [April 25, 2019, 5:18pm UTC](https://discourse.julialang.org/t/proposal-for-sharedfunctions-jl-package-for-optional-dependency-management/23526 "2019-04-25T17:18:42Z")\
**Posts on this page:** 1\
**Showing post:** 38

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**Author:** ![tkf](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tkf/32/17635_2.png) [@tkf](https://discourse.julialang.org/u/tkf)\
**Post date:** [April 27, 2019, 1:01am UTC](https://discourse.julialang.org/t/proposal-for-sharedfunctions-jl-package-for-optional-dependency-management/23526/38 "2019-04-27T01:01:42Z")

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I _think_ I found a super simple solution.

The key observations are:

1. Each package has a UUID
2. `isbitstype(UUID)` hence a UUID can be used as a type parameter

So, the idea is to define a “universal entry point function”:

```julia
module IndirectImports
    struct IndirectFunction{uuid, name} end
end

```

which can be used to refer to a function in a package without importing it. An example usage is:

```julia
module Upstream
    using UUIDs
    using ..IndirectImports: IndirectFunction
    const upstream_uuid = UUID("332e404b-d707-4859-b48f-328b8b3632c0")
    const fun = IndirectFunction{upstream_uuid, :fun}
end # module

module Downstream
    using UUIDs
    using ..IndirectImports: IndirectFunction
    const upstream_uuid = UUID("332e404b-d707-4859-b48f-328b8b3632c0")
    const fun = IndirectFunction{upstream_uuid, :fun}

    struct DownstreamType end
    fun(::DownstreamType) = "hello from Downstream"
end # module

@show Upstream.fun(Downstream.DownstreamType())

```

where the `Downstream` package defines a “function” in the `Upstream` package without importing the `Upstream`.

(The fact that `IndirectFunction{uuid, name}(...)` does not return a `IndirectFunction` is kind of bad but it’s not like this is forbidden…)

Does it work? I feel like I’m missing something as this is so simple. Maybe it is a too much burden on the Julia compiler to manage a possibly huge list of methods for `IndirectFunction`? Or maybe not?

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