Sharing global variables across modules in Julia - global-variables

Question

With the information kindly provided here: How to define global variables to be shared later in Julia I keep working on global variables in Julia.
file: global.jl
module Global
export data
data = zeros(Int32, 20, 12, 31, 24, 60, 5);
end
file: main.jl
# MAIN PROGRAM
# INCLUDE GLOBAL
include("global.jl")
import .Global
println(">> Main Before include test.jl")
println(">> ", Global.data[ 14, 1, 15, 18, 1, 1])
include("test.jl")
println(">> Main After include test.jl")
println(">> ", Global.data[ 14, 1, 15, 18, 1, 1])
file: test.jl
module Test
include("global.jl")
import .Global
println(" >> Inside Test")
println(" ", Global.data[ 14, 1, 15, 18, 1, 1])
Global.data[ 14, 1, 15, 18, 1, 1] = 123456
println(" ", Global.data[ 14, 1, 15, 18, 1, 1])
end
What I expect is that module Test will modify the Global array data and therefore it will later be reflected by main.jl. I am obviously still missing something as this is the output:
$ /usr/local/julia-1.2.0/bin/julia main.jl
>> Main Before include test.jl
>> 0
>> Inside Test
0
123456
>> Main After include test.jl
>> 0

Answer 1

The key issue you need to understand is that include works like copy-paste.
In you code you define module Global twice. Once in Main module, and once in Test module. These two modules have the same code but are separate (the latter is nested in Test module). See:
julia> Main.Test.Global.data[ 14, 1, 15, 18, 1, 1]
123456
julia> Main.Global.data[ 14, 1, 15, 18, 1, 1]
0
This is the way you should define the Test module to reuse the Global module defined earlier:
module Test
import ..Global
println(" >> Inside Test")
println(" ", Global.data[ 14, 1, 15, 18, 1, 1])
Global.data[ 14, 1, 15, 18, 1, 1] = 123456
println(" ", Global.data[ 14, 1, 15, 18, 1, 1])
end