I'm working on some Julia scripts and recently needed to write some utility functions usable from multiple files. I could be very careful with includes to make sure the file is included exactly once when needed, but that seemed rickety to me. I wanted it to be like a package I could confidently bring in with a using directive. Unfortunately this doesn't seem to be common in the Julia ecosystem and only really became possible (?) recently.
I had to make a subdirectory for the utility package containing a separate project with its own metadata. So the MyModule subdirectory had a Manifest.toml, Project.toml, and src subdirectory, containing MyModule.jl. The metadata files were created by the package manager, but I had to edit Project.toml to give the package a name and uuid. Then in the package environment for the root project, I ran develop MyModule to add the utility package as a development/local dependency.
