Handling of package inter-dependency

New to Julia
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11

Since there is no minimal working example (MWE), I could not figure out what you really wanted to do. (Please read: make it easier to help you)

However, I thought that possibly you would like to do something like this. Please take a look at the MWE below.

Input:

module SCI

export Problem, Algorithm_A, Algorithm_B, solve

abstract type AbstractProblem end
struct Problem{T} <: AbstractProblem x::T end

abstract type AbstractAlgorithm end
Base.@kwdef struct Algorithm_A{T} <: AbstractAlgorithm a::T = 2.0 end
Base.@kwdef struct Algorithm_B{T} <: AbstractAlgorithm a::T = 3.0 end
default_algorithm(prob::Problem) = Algorithm_A()

struct Solution{R, P<:AbstractProblem, A<:AbstractAlgorithm} result::R; prob::P; alg::A end
solve(prob::AbstractProblem) = solve(prob, default_algorithm(prob))
solve(prob::AbstractProblem, alg::AbstractAlgorithm) = Solution(alg.a * prob.x, prob, alg)

"""
Here, `Base` module plays the role of `COM` package.
SCI module can define the method of 
`Base.show` (≈ `COM.show`) function for `SCI.Solution` type.
"""
function Base.show(io::IO, sol::Solution)
    result = """
    Problem:   $(sol.prob)
    Algorithm: $(sol.alg)
    Result:    $(sol.result)
    """
    print(io, result)
end

end

using .SCI
@show prob = Problem(1.5)
println()
println(solve(prob))
println(solve(prob, Algorithm_B()))

Output:

prob = Problem(1.5) = Problem{Float64}(1.5)

Problem:   Problem{Float64}(1.5)
Algorithm: Algorithm_A{Float64}(2.0)
Result:    3.0

Problem:   Problem{Float64}(1.5)
Algorithm: Algorithm_B{Float64}(3.0)
Result:    4.5

Additional input:

module SCI2 # extension of SCI module

export Problem2, Algorithm_C

using ..SCI: SCI, AbstractProblem, AbstractAlgorithm, Solution

struct Problem2{T} <: AbstractProblem x::T; y::T end
Base.@kwdef struct Algorithm_C{T} <: AbstractAlgorithm a::T = 2.0; b = 3.0 end
SCI.default_algorithm(prob::Problem2) = Algorithm_C()
SCI.solve(prob::Problem2, alg::Algorithm_C) = Solution(alg.a * prob.x + alg.b * prob.y, prob, alg)

end

using .SCI2
@show prob2 = Problem2(10.0, 1.0)
println()
println(solve(prob2))

Output:

prob2 = Problem2(10.0, 1.0) = Problem2{Float64}(10.0, 1.0)

Problem:   Problem2{Float64}(10.0, 1.0)
Algorithm: Algorithm_C{Float64}(2.0, 3.0)
Result:    23.0

In the above example I don’t define AbstractSolution type, nor did I make Solution a subtype of it. But you can define it, and then define another Solution type as a subtype of it in SCI2 module, and also define how to display objects of another Solution type. Many other extensions are also possible.

See also Function depending on the global variable inside module - #10 by genkuroki