How can I structure a project in multiple modules and have code run in them?

[fatteneder]

@bertulli

1. This way I need to load all the submodules at once inside ARMCortexM4Model. Can I selectively load just some of them, without modifying ARMCortexM4Model.jl every time? In other words, can I just say

Yes. The export Utils inside ARMCortexM4Model.jl only exports the name Utils, but does not export all the names Utils it self would export.
Hence, when you write using ARMCortexM4Model you can then use Utils.greet() instead of ARMCortexM4Model.Utils.greet(). If you also add export greet inside Utils.jl then you could write

julia> using ARMCortexM4Model

julia> using Utils

julia> greet()

@bertulli

2. Is there a way to declare more than one module in a single project?

Yes and no: A package (as generated by running Pkg.generate("MyPackage")) defined as a folder with a name MyProject containing a Project.toml file referring to MyProject (and optionally a Manifest.toml) and then a src/MyProject.jl file. Let’s call this a toplevel package, although it really is an environment (or project), I think, because it tracks all the dependencies used in it and it happens so that one if it is also called MyProject. Think of a project like a virtualenv in python, if you happen to know that …
There are then two ways to add more modules:

1. Recommended: Add submodules to MyProject as I did it above, which you can optionally reexport. See also the @reexport macro from Reexport.jl.
2. Add another package with Pkg.generate("MyPackage/Utils"). You must then tell your toplevel package to develop this package, e.g. run Pkg.develop(path="./Utils").

@bertulli

3. I read ] dev is used to develop a package. But now I don’t understand how: if I am bounded to develop a single package at a time, there’s actually no need to dev it in the first place. I thought I could dev all the modules I was working on, so that I can independently include them in my working scripts, and use Revise if I needed to modify the modules’ code.

The dev is needed so that Revise.jl can track its code. The other alternative is to add a package, but for that to work the package needs to be git repository. The way of adding another module through dev is really only meant for local development of packages and its dependencies and/or mono repos like Makie where they develop multiple packages inside one toplevel package.

In case you haven’t discovered it yet, here is a link to the docs of Pkg which talks packages, environments a bit more: 1. Introduction · Pkg.jl

I also must admit I am not a big fan of this kind of project organization and I feel like I am seeing this question being asked way too often. Perhaps this is an indication that things could be simplified or made more user friendly, but then I did not think how …

@bertulli

Thanks, IIUC this also has the advantage of allow the re-loading of the data at your discretion. But just to better understand how modules work, can I do the same using “just” them?

Sorry, didn’t understand the question.