Layered Design in Go

https://jerf.org/iri/post/2025/go_layered_design/

by misonic • 1 year ago

141 39 1 year ago

__s• 1 year ago

Kind of reminds me of the concept of spheres in randomizers

great blog post! also this website has a lot of incredible posts, if you like learning about functional programming, you should check out

https://jerf.org/iri/blogbooks/functional-programming-lesson...

rapidlua• 1 year ago

Packages may not circularly reference each other.

Actually possible with go:linkname.

jerf4• 1 year ago

Fair, but I think we can classify that under "unsafe" and ignore it under normal circumstances. I can also say things like "Go doesn't have pointer arithmetic" with a straight face, even though unsafe permits pointer arithmetic just fine. If you're programming with that routinely, you're out of the bounds of my advice for architecture anyhow. Whether for good or bad reasons would be left as an exercise for the architect in question.

ncruces4• 1 year ago

Looking at the diagram for the SQLite VFS page I didn't think I was going overboard with designing my driver around 3 packages: https://sqlite.org/vfs.html

One layer wraps SQLite C API, below it lives a pure Go VFS, and above all that database/sql driver.

Even this coarse split (with a collection internal packages, the bigger one of them “utils”) is enough to need various band-aids to accommodate the impossibility of circular dependencies.

I honestly don't think it helps much.

At the module level, there are obvious benefits from the impossibility. Just like all the pain around v2 modules can be justified, even if I find it annoying.

When packages are also the only layer at which you can enforce visibility, it becomes worse.

pjmlp2• 1 year ago

Looks like I am reading a book about Yourdon structured method.

jerf4• 1 year ago

Since I meant this just as a "how I do it" post I suppose I forgot the disclaimer that I'm not particularly claiming to have invented anything or to be the first. Indeed to a large degree I consider myself just to be following the grain of Go and hardly doing anything myself.

That said, after some quick googling around, I don't think I feel bad not knowing what Yourdon design is, as it seems to be somewhat proprietary and behind paywalls, so it's hard for me to tell if there's much similarity. Certainly it has a lot of stuff I tend to eschew; lots of references to diagrams and state charts and such. I tend to prefer a more "agile but wait before you panic I mean 'original' agile not 'scrum' or whatever other abomination it was turned into", my formal method is more based around exploring the design space with extensive unit tests and code rather than that sort of up-front design.

pjmlp2• 1 year ago

It was a common way to structure enterprise C code during the 1990's, and the snarky remark is how the anti-enterprise culture from Go ends up adopting the same big corporation principles, given enough wind behind its sails.

Yourdon is the big wave of enterprise methodologies immediately predating the OOP wave with Booch, UML, GoF and friends.

I can gladly bet there are some Go pattern books around the corner as well.

As for the book paywall, it is certainly available in many libraries, given its age.

kubb• 1 year ago

Cool description of how jerf thinks about packages and how he deals with circular dependencies!

nickcw• 1 year ago

In my opinion, not allowing circular dependencies is a great design choice for building large programs. It forces you to separate your concerns properly.

If you get a circular dependency something is wrong with your design and the article does a good job on how to fix them.

I sometimes use function pointers which other packages override to fix circular dependencies which I don't think was mentioned in the article.

My only wish is that the go compiler gave more helpful output when you make a circular dependency. Currently it gives a list of all the packages involved in the loop which can be quite long, though generally it is the last thing you changed which caused the problem.

ternaryoperator• 1 year ago

In the abstract, I think I agree with you. But in reality, what I see is that go projects use far fewer packages than, say, programs in Java. Many go projects use one or two omnibus packages--principally, I expect, to avoid having to worry about circularity issues.

By forcing this design pattern on developers (something no other language does), I think the result has been overall worse code rather than better.

Perhaps a warning, rather than stop-the-compiler error would have been a better choice. Not sure.

Either way though, I wholly agree that the compiler gives too little information, which is curious because it knows the needed data and should easily be able to present it in a useful way.

jen202• 1 year ago

I see the opposite in most Java programs: poor organization with packages based on a type of thing (eg models, controllers) rather than related behaviors.

Go doesn’t have warnings, which is great - if something is worth warning about, it is also worth erroring about. It never ceases to amaze me when a brand new JavaScript project spits out dozens of errors after pulling in a common library, and everyone thinks that is ok.

wavemode5• 1 year ago

If you get a circular dependency something is wrong with your design

Packages not being able import from each other circularly is purely a compiler limitation. It says nothing about the realities of software development.

This notion stems from the idea that software design is inherently hierarchical, and that there is always a clear "higher level" and "lower level" between every possible software module.

What I've found in practice is that this is a fictional concept. Circularity between modules is very common and natural (especially as business requirements change over time). The workarounds people invent to avoid circularity literally always result in a codebase that is harder to understand and maintain, rather than easier.

It forces you to separate your concerns properly.

Nah. It's not separation of concerns, it's separation of implementation. Two functions that in every other way shape and form deal directly with the same concepts, end up needing to be in separate modules purely because they differ in the functionality they import. And if later their imports change, they may need to be moved again. Which means implementation details are leaking into your design, which makes code less discoverable (since you now need to know implementation details in order to reasonably predict where a given function might be defined).

politician• 1 year ago

I prefer extremely fast compile times.

9rx5• 1 year ago

Circularity between modules is very common and natural

In theory, but in practice it isn't because there are very few language that do not see software design as being hierarchical. That stems primarily from most languages being based on a hierarchical filesystem, which imposes a hierarchical view of the world at the very core. Circular references in languages that are hierarchical end up being very awkward.

There are a small handful of languages that reject all things hierarchical, including the filesystem, but they are few and far between and most probably have never heard of them and they certainly aren't what you are going to find in production. For better or worse, we've settled on a hierarchical model.

layer8• 1 year ago

[The following is intended as language-agnostic.]

It’s useful to distinguish between interface and implementation dependencies. I agree that there shouldn’t be circular interface dependencies between modules. The absence of circular interface dependencies allows separate compilation of modules. It also means that at least in principle, the implementations can be made non-circular (can be refactored to non-circular without breaking any of the existing interfaces). But it’s often okay for the implementation of A to depend on the interface of B, and at the same time the implementation of B to depend on the interface of A, as long as there is no mutual dependency between the interfaces of A and B.

euroderf2• 1 year ago

In my opinion, not allowing circular dependencies is a great design choice for building large programs.

I have a hobby project with maybe 20 packages involved. Circular dependencies were getting harder and harder to solve.

What worked in this situation was to separate the whole hairball into two layers. The packages in the app layer could import packages from the utilities layer, but not vice-versa.

This introduced enough structure to simplify the removal of circularities and prevent new outbreaks.

ncruces4• 1 year ago

But, don't you know you can't have a utils package either?

A package must implement one functionality, and it must be clear from the short import name what that functionality is.

A package is also the only way to enforce visibility (and often, with that, other useful properties like immutability).

So packages can't be too big, or too generic, but they can't also be too small, or too specific.

I also have 2 (or 3?) layers, and a utils package, and the packages are huge, and yet I need various cheats to allow cyclic dependencies, and have some repetition with other tricks to avoid some of it.

It's the real world, and guess what, the very well designed standard library does… all of the above too.

shizcakes• 1 year ago

One bonus technique related to the “move to a third package” advice: generating many of your model structures (SQL, Protobuf, graphql, etc) allows you to set up obvious directionality between generated layers and to provide all generated code as “base packages” to your application code, which then composes everything together.

Prior to this technique we often had “models importing models circularly” as an issue but that’s entirely disappeared due to the introduction of the structural additional layer.

darioush• 1 year ago

A funny quirk about golang is you cannot have circular dependencies at the package level, but you can have circular dependencies in go.mod

The tl;dr is don't do that either.

0xjnml• 1 year ago

go.mod files have no dependencies, so neither they can have circular dependencies.

go.mod files just list the dependencies of their respective package.

Layered Design in Go

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