I tried the import option in the file menu, but the only option is to import a binary project, and it just seems to open the project I select, not allow me to pick and dynamically link to a specific module or file from that project.
To clarify…
What I’m looking for is picking a module file that I have created as a function library and link to it, not include it statically, so if I change something in the original, the changes are available in the project that links to it.
Export the module to a file, delete it from your project, then drag the newly-exported file back into the project while holding down command-option (control-alt in Windows, I think). The module will reappear in your project in italics meaning that it is now external to your project and any changes will propagate automatically to any other project that uses the same module externally.
There’s no place to put an include directive that would function anything like C’s include near the top of an implementation or header file.
If you make a module / class external then you can share it around among as many projects as you want and every project that uses it gets what ever updates.