What does this syntax (using .Filename) mean?

New to Julia
1

Can someone explain this syntax (in REPL)?

include("Filename.jl")
using .Filename

I can sort of understand the first, but what is the . in front of Filename mean?

2

I’ve not used that format before, but a quick read of the module documentation indicates that you can access module hierarchy’s using the “.” notation. LOL, I didn’t even know you could have submodules !

https://docs.julialang.org/en/v1/manual/modules/#Submodules-and-relative-paths

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3

Actually the filename has nothing to do with using .Filename. Filename is expected to be a module defined in the file.

4

You can see the effect of using .ModuleName without needing to worry about include at all. Here’s a simple example:

julia> module MyModule
         export foo
         
         foo() = println("hello world")
       end
Main.MyModule

Here I’ve defined a module which exports one function (foo). But I’ve only defined that module, I haven’t using-ed it, so I don’t yet have access to that exported function:

julia> foo
ERROR: UndefVarError: foo not defined

To get foo into my current namespace, I need using. But if I just do using MyModule, it doesn’t work:

julia> using MyModule
ERROR: ArgumentError: Package MyModule not found in current path:

That’s because using MyModule tells Julia to look for some module with that name in a file in the LOAD_PATH or in the current package environment. That’s not what we want–we already defined that module.

Instead, we can do using .MyModule which says "find a module named MyModule which is already defined in the current namespace (in this case, in Main), and activate it:

julia> using .MyModule

julia> foo()
hello world

You can add additional dots to activate modules in a parent module:

julia> module A
         export bar
         
         bar() = println("bar")
         
         module B
           using ..A
           
           function f()
             println("Calling `bar` which was defined in the parent module `A`:")
             bar()
           end
         end
       end
Main.A

julia> A.B.f()
Calling `bar` which was defined in the parent module `A`:
bar
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