Proposal for SharedFunctions.jl package for optional dependency management

Internals & Design
38

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”:

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:

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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