Yes. But I want to make clear that you are still using global state for all uses within the project itself. The library can be implemented in whatever way. For example, setting the pointer in a global variable on API entry ;-)
> That doesn't solve the problem at all.
WHICH problem? I don't think there is one.
> Indeed, and they're seen as bad practice for the same reason as global state in general.
This is foolish. There is no problem with global state. Global state is a fact of life. Your process has one address space. It has (probably) one server socket for listening to incoming request. It has (probably) one graphics window to show its state. Whenever you have more (e.g. file descriptors, memory mappings, ...), well then you have a set of that thing, but you have ONE set :-). And so on.
You are not writing a thousand pseudo-isolated programs. But ONE. One entity composed of a fixed number of parts (i.e. modules, code files) that work together to do what must be done.
Why add indirection? Why make it hard to iterate over all open file descriptors? Why thread a window handle through 15 layers of function calls when you have only one graphics window? It adds a lot of boilerplate. It even brings some people to invent hard to digest concepts like monads or objects just to make that terrible code manageable. It makes the code unclear. Someone once described it with this analogy, "I don't say ''I'm meeting one of my wives tonight'', unless I have more than one".
But if we believe in using libraries then often our project will itself be a library.
> The library can be implemented in whatever way. For example, setting the pointer in a global variable on API entry ;-)
And then you have the problem I mentioned: if there is a diamond dependency on your library then the thing using it will break.
> WHICH problem? I don't think there is one.
The problem of not being able to break down your project and understand it piecemeal.
> Global state is a fact of life. Your process has one address space. It has (probably) one server socket for listening to incoming request. It has (probably) one graphics window to show its state.
All those global things are a common source of bugs, as different pieces of the program make subtly different assumptions about them. Perhaps a certain amount of global state is unavoidable. That's not an argument against minimizing it.
> You are not writing a thousand pseudo-isolated programs. But ONE. One entity composed of a fixed number of parts (i.e. modules, code files) that work together to do what must be done.
If you write a program that can only be understood in its entirety, you'll be unable to maintain it once it becomes too big to fit in your head. Writing a thousand isolated functions gives you something much easier to understand and scale.
That's just incredibly untrue. It's FUD spread by OOP and FP zealots.
> All those global things are a common source of bugs, as different pieces of the program make subtly different assumptions about them.
Do you want to say that my logging routine is more complex because my windowing handle is stored in a globally accessible place?
> Perhaps a certain amount of global state is unavoidable. That's not an argument against minimizing it.
My advice is to make clear what the data means. Make it simple. Don't put a blanket over what's already hard to grasp.
If your logging routine touches your windowing handle that certainly makes it more complex. If I'm meant to know that your logging routine doesn't touch your windowing handle, that's precisely the statement that it isn't global data.
In terms of the relational data model, it is global data because there is always one, and only one, of it.
How about making the project good first? Let's try to get something done instead of theoretizing.
Regarding the size, clearly wrong. It depends a lot on the library. A windowing or font rastering library will be a lot larger than your typical application.
And for libraries that are much smaller than the application itself, why bother depending on them? (Anecdote, I heard the Excel team in the 90s had their own compiler).
At the most basic level, if project A makes use of library B and library C, then you want to be able to verify the behaviour of library B and library C independently and then make use of your conclusions when analysing project A. But if library B and library C use global state then you can't have any confidence that that will work. E.g. if both library B and library C use some other library D that has some global construct, then they will likely interfere with each other.
> Another possibility would be to have subproject-wide global state, and passing a pointer only to library API calls. The latter is also the most realistic case since most libraries take pointer handles.
At that point you're not using global state in the library, which was the point.
> you can always opt for process- or thread-wide global state
That doesn't solve the problem at all.
> Also called "singleton" in OOP circles. Singletons are nothing but global data with nondeterminstic initialization order and superfluous syntax crap on top.
Indeed, and they're seen as bad practice for the same reason as global state in general.