Julia 1.1.1 - absolutely global variables - julia

Question

I am coming from Fortran and I use global vectors of data over the full program. Usually I declare a module:
module xyz
real, allocatable :: vector(:,:,:) ! a 3 dim vector, undefined
end module
Now, in some place, let say Subroutine (Function) A, I am allocating memory for it and initialize to some values:
allocate(vector(10,20,30))
vector = ran()
Now, in any other unit of the program (Subroutine or function B, C, D...), if I am using the module, i.e:
using xyz
The above declared vector is available.
I was not able to obtain this behavior in the new technological wonder Julia 1.1. The scope rules are just giving a headache.

Answer 1

In Julia the rules for accessing variables from other modules are explained in detail here.
The key issues in your situation are the following things:
a variable is visible after using only if it is exported in the module
you are allowed to access the variable in other modules
you are not allowed to rebind a variable from other modules
This means that global variable binding creation operation is private to the module.
Here is a simple example module definition:
module M
export x
x = Int[]
function rebindx()
global x = Int[]
end
end
now assume you define and later use it in REPL (it could be any other module)
julia> module M
export x
x = Int[]
function rebindx()
global x = Int[]
end
end
Main.M
julia> using .M
Now you can access x:
julia> x
0-element Array{Int64,1}
julia> push!(x, 1)
1-element Array{Int64,1}:
1
julia> x
1-element Array{Int64,1}:
1
julia> x[1] = 10
10
julia> x
1-element Array{Int64,1}:
10
But not rebind x:
julia> x = 0
ERROR: cannot assign variable M.x from module Main
However, you can call a function defined inside M module to change the binding of x like this:
julia> x
1-element Array{Int64,1}:
10
julia> M.rebindx()
0-element Array{Int64,1}
julia> x
0-element Array{Int64,1}
This was possible because rebindx was defined inside module M so it has the right to change the binding of variable x defined in this module.