Languages like Python, Rust, C# or even Java have module systems that I find are more restrictive, but much easier to follow. You always have the pertinent information at hand. Each file containing code clearly tells you two crucial pieces of information:
1. Where the code fits in the greater picture
2. Where the dependencies of the code in a file come from
Python, whose module story is actually pretty poor, is still easier to follow than Julia, because it just matches the file/directory structure. You can reason about the hierarchy of a python library by just navigating the directories. In a normal python project, each file is one module and it's dependencies are clearly specified as imports.
Rust relies on the file system as well, and much better defined rules than Python. I find this great, because the file system is already hierarchical and we are used to the way it works. When I open a file in a Rust project, I know immediately where it fits in the hierarchy - because it is implied from the file system. Rust gives you a bit more flexibility in that you can define submodules in each file.
C# & Java qualify the namespaces fully in each file. While the file structure is not as clear anymore at the file system level, a single file contains all the information necessary to determine where the code fits in and where it's dependencies come from.
Now let's take Julia:
A single module will be often split across multiple files. Since they share a single namespace, the imports happen at the top level where the module is defined and includes all it's source files. When you open a source file, you have zero information where all the functions and data types are coming from (or where they are going for that matter).
I see the following pattern systematically emerge in Julia code:
- A function is defined in file A
- File A is `included` in file B, where it forms part of module X
- It is then imported into module Y in file C, but it is not actually used there
- As it is finally used in file D, which is `included` in module Y in file C itself
The problem is that there is no link from file A to file B, or module X for that matter. File A could be part of a dozen modules, or zero. Neither is there a link between the usage of the function in file D and where it is coming from. You actually have to find all the places where file D is included, and then check what flavor of the function does each location import. The relationships are established at some indeterminate level in the hierarchy.
Again, don't get me wrong, this is just a wart on an otherwise very pleasant language. I wouldn't be complaining if I weren't using it.