Constraints in Go

i have been writing Go exclusively for 5+ years and to this day i use generics only in a dedicated library that works with arrays(slices in Go world) and provides basic functionality like pop, push, shift, reverse, filter and so on.

Other than that, generics have not really solved an actual problem for me in the real world. Nice to have, but too mush fuss about nothing relevant.

Honestly so many things profit from generics, e.g. ORM code was very awkward before especially when returning slices of objects as everything was []any. Now you can say var users []User = orm.Get[User](…) as opposed to e.g var users []any = orm.Get(&User{}, …), that alone is incredibly useful and reduces boilerplate by a ton.

ORM is anti-pattern and reducing boilerplate is bad.

Just checked, in my current project, the only place where I use generics is in a custom cache implementation. From my experience in C#, generics are mostly useful for implementing custom containers. It's nice to have a clean interface which doesn't force users to cast types from any.

understandable. thee are always valid uses cases. although ORM in Go is not something that is widely used.

I agree. The best language to handle data in a RDBMs is SQL, and in that case the best language to handle application logic is Go (or Kotlin, Python or whatever). So there must be some meeting point. Handling everything in Go is not optimal, and all in sql not always practical. So how to avoid redundant data description ? I often have structs in a model Go file that reflect queries I do, but that's not optimal since I tend to have to repeat what's in a query to the language and the query to struct gathering is often boilerplate. I also almost can reuse the info I need for a query for another query but leave some fields blank since they're not needed.. the approaches are not optimal. Maybe a codegen sql to result structs / gathering info ?

Could you expand on this?

I don't like ORM because in my experience you inevitably want full SQL features at some point but not sure if you have the same issues in mind or not

ORM is for object-relation mapping. Go is not object-oriented language and OOP-patterns are not idiomatic Go, so using ORM for Go cannot be idiomatic. That's generic answer. As for more concrete points:

1. Mapping SQL response to maps/structs or mapping maps/structs to SQL parameters might be useful, but that's rather trivial functionality and probably doesn't qualify as ORM. Things get harder when we're talking about complex joins and structs with relationships, but still manageable.

2. Introducing intermediate language which is converted to SQL is bad. Inevitably it will have less features. It will stay in the way for query optimisations. It'll make things much less obvious, as you would need to understand not only SQL, but also the process of translating intermediate language to SQL.

3. Automatic caching is bad. Database has its own caching and if that's not enough, application can implement custom caching where it makes sense.

In my opinion the only worthy database integration could be implemented with full language support. So far I only saw it with C# LINQ or with database-first languages (PL/SQL, etc). C# and Go are like on opposite spectrum of language design, so those who use Go probably should keep its approach by writing simple, verbose and obvious code.

I sometimes wonder if they should have implemented generics. On the one hand you had a group of people using go as it was and presumably mostly happy with the lack of generics. On the other side you have people (like me) complaining about the lack of generics but who were unlikely to use the language once they were added.

It's very subjective but my gut feeling is they probably didn't expand their community much by adding generics to the language.

Containers are sort of the leading order use of generics: I put something in and want to statically get that type back (so no cast, still safe).

Second use I usually find is when I have some structs with some behavior and some associated but parameterizable helper. In my case, differential equations together with guess initializers for those differential equations. You can certainly do it without generics, but then the initial guess can be the wrong shape if you copy paste and don't change the bits accordingly. The differential equation solver can then take equations that are parameterized by a solution type (varying in dimension, discretisation and variables) together with an initializer that produces an initial guess of that shape.

Finally, when your language can do a bit of introspection on the type or the type may have static methods or you have type classes, you can use the generic to control the output.

Basically, they are useful (like the article implies) when you want to statically enforce constraints. Some people prefer implicitly enforcing the constraint (if the code works the constraint is satisfied) or with tests (if the tests pass the constraint is satisfied). Other people prefer to have the constraints impossible to not satisfy.

I think a lot of the people who wanted generics wanted them more to be like C++ templates, with compile time duck typing. Go maintainers were unwilling to go that route because of complexity. However, as a result, any time I think "oh this looks like it could be made generic" I fall into a rabbit hole regarding what Go generics do and dont allow you to do and usually end up copy pasting code instead.

Generic containers are needed in some cases. Using generic containers with interface{} is very slow and memory-intensive. Not a problem for small containers, but for big containers it's just not feasible, so you would need to either copy&paste huge chunks of code or generate code. Compared to those approaches, generic support is superior in every way, so it's needed. But creating STL on top of them is not the indended use-case.

> reducing boilerplate is bad

Programming is about building abstractions, abstractions are a way to reduce boilerplate.

Why do we need `func x(/* args / ) { / body */ }`, when you can just inline the function at each callsite and only have a single main function? Functions are simply a way to reduce boilerplate by deduplicating and naming code.

If 'reducing boilerplate is bad', then functions are bad, and practically any abstraction is bad.

In my opinion, "reducing boilerplate is bad in some scenarios where it leads to a worse abstraction than the boilerplate-ful code would lead to".

I think you have to evaluate those things on a case-by-case basis, and some ORMs make sense for some use-cases, where they provide a coherent abstraction that reduces boilerplate... and sometimes they reduce boilerplate, but lead to a poor abstraction which requires more code to fight around it.

> Go is not object-oriented language

That is most definitely not true. Go just uses composition instead of inheritance. Still OOP, just the data flow is reversed from bottom to the top.

I find libraries like sqlx more than enough. Instead of a full-blown ORM, they simply help hydrate Go structs from returned SQL data, reducing boilerplate. I prefer the repository pattern, where a repository is responsible for retrieving data from storage (using sqlx) using simple, clean code. Often, projects which use full-blown ORMs, tend to equate SQL table = business object (aka ActiveRecord) which leads to lots of problems. Business logic should be completely decoupled from underlying storage, which is an implementation detail. But more often than not, ORM idiosyncracies end up leaking inside business logic all over the place. As for complex joins and what not, CQRS can be an answer. For read queries, you can write complex raw SQL queries and simply hydrate the results into lightweight structs, without having to construct business objects at all (i.e. no need for object-relational mapping in the first place). Stuff like aggregated results, etc. Such structs can be ad hoc, for very specific use cases, and they are easy to maintain and are very fast (no N+1 problems, etc). With projects like sqlx, it's a matter of defining an additional struct and making a Select call.

Well, generics are mostly meant for library code. Just because you don't need it, doesn't mean that code you use doesn't need it.

Not liking ORM I can understand, db table <-> object impedance mismatch is real, but "reducing boilerplate is bad" is an interesting take.

Can you elaborate and give some examples of why reducing boilerplate is generally "bad"?

There’s an existing ecosystem that already works with the constraints of not having generics. If you can write all your code with that, then you won’t need generic much. That ecosystem was created with the sweat of library authors, dealing with not having generics and also with users learning to deal with the limitations and avoid panics.

Generics have been tremendously helpful for me and my team anytime we are not satisfied with the existing ecosystem and need to write our own library code. And as time goes on the libraries that everyone uses will be using generics more.

Not the person you’re replying to. The orm sucks because as soon as you go out of the beaten path of your average select/insert/update/delete, you are inevitably going to end up writing raw sql strings. Two cases in point: postgres cte and jsonb queries, there are no facilities in gorm for those, you will be just shoving raw sql into gorm. You might as well stop pretending. There’s a difference between having something writing the sql and mapping results into structs. The latter one can be done with the stdlib sql package and doesn’t require an „orm”.

There are two things an sql lib must do to be very useful: prepared statements and mapping results. That’s enough.

> From my experience in C#, generics are mostly useful for implementing custom containers.

That's my experience as well in C# - most of other usages of generics are painful to maintain in the long run. I've had most problems with code that joins generics with inheritance.

You haven’t answered my question at all.

The parent comment made two claims: ORM not great (I agree) and “boilerplate reduction bad” which still needs some elaboration

Perhaps you have to yet use a good ORM? I could probably count on my fingers the times I had to drop to raw SQL in EFCore. Even when you do that you can still have mapped results, which reduces boilerplate.

>> Go is not object-oriented language

> That is most definitely not true.

I think at best, you could say that Go is a multi-paradigm language.

It's possible to write Go in an object oriented style.

It's also possible to write programs with no methods at all (although you'd probably have to call methods from the standard library).

That's in contrast to a language like Java or Ruby where it's actually impossible to avoid creating objects.

Unless you happen to want to warm up the CPU, there is very little Go code that is possible to write that does anything useful without OOP concepts, like interfaces, methods and dynamic dispatch.

Creating objects on the heap isn't the only defining feature how a language does OOP or not.

I think "oh this looks like it could be made generic" is the wrong time to convert to generics.

You should convert when you reach the point "I wish I had that code but with this other type". Even then, sometimes interfaces are the right answer, rather than generics.

What I mean is reducing boilerplate is not something one should strive to achieve. It is not bad in the sense that one should introduce more boilerplate for the sake of it. But reducing boilerplate for the sake of it is not good thing either.

If you need to make code more complex just to reduce boilerplate, it's a bad thing. If you managed go make code simpler and reduced boilerplate at the same time, it's a good thing.

And boilerplate might be a good thing when you need to type something twice and if you would make error once, the whole thing wouldn't work, so basically you'll reduce the possibility of typo. It might look counter intuitive. Just unrelated example: recently I wrote C code where I need to type the same signature in the header file and in the source file. I made mistake in the source file, but I didn't make the same mistake in the header file and the whole program didn't link. I figured out the mistake and corrected it. Without this boilerplate it's possible that I wouldn't notice the mistake and "helpful" autocomplete would keep the mistake forever. That's how HTTP Referer header made it into standards, I guess.

The most frequent use case I and my coworkers run into where we use them is when we want type covariance on a slice.

I.e., when you want to write a function that take some slice of any type T that implements interface I, such that []T is a valid input instead of just explicitly []I.

Having recently had to work on a Go project for the first time, I think I agree with you here. I'd tried Go a little bit when it came out, had zero interest in what it offered, and then when I was asked to work on this project a couple months ago I thought it would be fun to try it out again since I had read the language had improved.

No, it still feels like programming with a blindfold on and one hand tied behind my back. I truly don't get it. I've worked with a lot of languages and paradigms, am not a zealot by any means. Other than fast compiles and easy binary distribution, I don't see any value here, and I see even experienced Go programmers constantly wasting time writing unreadable boilerplate to work around the bad language design. I know I must be missing something because some people much smarter than me like this language, but... what is it?

I answered it, you just don’t see it. One ends up with the boilerplate anyway as soon as one attempts to step out of the usual crud path. There’s no gain, there’s no difference in templating an sql string vs fighting an orm api.

I’m doing this job for 25 years and I haven’t seen a good orm. Sorry. Look, linq is nice. But linq is not enough of a productivity gain to switch the whole stack from go to .net. I used linq 15 years ago extensively and it feel like magic. But then again, how would you model jsonb select for a variable set of of properties and include nested or and and conditions using its notation? Maybe you could but how much longer is it going to take you rather than templating a string?

Go has objects, but objects alone does not imply orientation. For that, you need message passing.

C# generics are way more powerful than that when it comes to writing high-performance or just very, err, generic code. Generic constraints and static interface members are immensely useful - you can have a constraint that lets you write ‘T.Parse(text[2..8])’.

They are far closer to Rust in some areas (definitely not in type inference sadly, but F# is a different story) than it seems.

Of course if one declares that they are an expert in a dozen of languages, most of which have poorly expressive type systems, the final product will end up not taking advantage of having proper generics.

Mad LoCs, dude, gotta make alotta lines, that’s what productivity is!

here you go.

func Ptr[T any](v T) *T { return &v }

That's kinda the point. Generics are mostly a library concern, improving end-user experience and performance. End-user creation of generic types is relatively rare, and you can use them in very simple ways and that's almost always good enough because you don't need them to be maximally correct, only good enough.

For libraries (that adopt generics): yes they can be complicated. But using them is mostly zero-effort and gets rid of a ton of reflection.

My most common use of generics is when testing — check out my library for typesafe test comparisons. I find it really useful because I like having readable helpers for asserting in tests, but I also want compiler errors if I refactor things.

https://github.com/peterldowns/testy

this is wild because i use parametric polymorphism by writing `forall` in basically every Haskell PR i do for work ever

i think Go having a pretty bad implementation of parametric polymorphism (a programming concept from the 70s) is probably the root cause here

> I see even experienced Go programmers constantly wasting time writing unreadable boilerplate

if it is unreadable, in Go, probably the most readable language used today, i would question the aforementioned experience.

Unfortunately not everyone shares that opinion of their restricted use-cases.

I've seen ~100 line HTTP handler methods that are implemented using generics and then a bunch of type-specific parameters inevitably get added when the codepaths start to diverge and now you've got a giant spaghetti ball of generics to untangle, for what was originally just trying to deduplicate a few hundred lines of code.

What you're doing right now is called "coping".

tbh I'll still take it over a similar Gordian knot with interfaces. At least you can tell the restrictions are met at compile time, rather than silently failing at runtime because you (and/or someone else in the past) didn't notice one edge case lodged somewhere surprising.

> Other than fast compiles and easy binary distribution, I don't see any value here, and I see even experienced Go programmers constantly wasting time writing unreadable boilerplate to work around the bad language design. I know I must be missing something because some people much smarter than me like this language, but... what is it?

If you "other than" two huge-for-many-use-cases good things, sure, it might look bad. ;)

But I would add good overall performance and in particular straightforward flexible concurrency support to the list of good things.

And IMO once you're in the set of "things with good perf" there's generally a lot of "boilerplate" of one sort or another anyway.

I mostly agree, hence the

> end up copy pasting code instead

bit of my original comment

Yeah that's fair. In terms of "things with good perf" I'd rather be writing C++ or Rust, but there are significant issues with using either of those on a large team.

I'm more comparing it against languages like Kotlin and Swift, or even Scala.

It might be nit picking, but that's more the ecosystem or tooling that's great. The language is mediocre, but it's what everyone gushes about.

I still remember people gaslighting everyone that any feature Go had was ESSENTIAL, and every feature Go didn't have was USELESS or too complicated for mere mortals "delivering value".

And the fast compiles at least are in big parts because the language is so horrendously basic. Can't get hung up on checking type constraints if you barely have any.

Any ORM worth it's salt has an escape hatch that allows you to do all those fancy raw SQL queries.

But the amount of queries that aren't fancy, and that an ORM is perfectly capable of abstracting away is (imho) 90% of all queries run.

Why make 90% or queries more tedious and error prone, just to make 10% slightly easier?

I don't think a language where for every 1 line of functionality, you need 3 lines of error handling boilerplate gets to be called readable.

Heck, Go went out of it's way to "subvert expectations" more than the last season of Game of Thrones.

99% of decent C-ish languages either do "String thing" or "thing: String", but Go is so fancy and quirky, it does "thing String" for no freaking reason. Don't get me started on the nightmare that is map types.

I like Go's error handling. The reader knows exactly which lines of code can encounter an error, and exactly how the error is handled.

I find that exception-based code is much harder to read. The happy path is clearer, but exceptional code paths are often completely obscured. It's harder to reason about what state the program is in when the exception is handled.

Exceptions have been a mistake, the alternative are Result types, a concept which predates go.

gorm just takes a pointer of your type and does reflection magic. It's worse than generica, I agree, but you don't get []any.

I felt the same way initially, but the language has grown on me. The turning point was writing a lot of Go, like full-time project work for a few months.

But as I've gotten older, I've started striving more and more for simplicity above all else, especially in systems design (disclaimer: I'm an SRE). Go is pretty good at being simple.

There are some things that still annoy me a whole bunch, though. Like - just one example - `fmt.Errorf` not being a first-class syntactic construct (or the difference between `%v` and `%w` in `fmt.Errorf`).

The libraries will, yes. But folks just using the libraries still won't need generics.

If you know your concrete types, they're just not that useful.

Even in home-grown libraries, I find generics to be a convenience rather than a necessity. It's useful to not have my library code so tightly coupled to my non-library code. But it does also come with a cost: every so often I have to check what the library actually does because being loosely coupled meant that iterations in the rest of the system didn't automatically have to involve the library, so the library code can get left behind.

Library authors were the main target group, I think.

Without generics, your library has to define interfaces that your users have to implement and it all gets a bit strange and unintuitive.

With generics you can write library code that is easier to use.

The thing I was worried about with this (adding generics) is that we'd start moving more towards the NPM Hell of everyone just writing plumbing code for imported packages. But thankfully that hasn't happened and idiomatic Go still tends to just use the standard lib and very few external packages.

I've been doing this job for over 30 years and I agree.

Entity Framework was the thing that made me spit the dummy with C#, uninstall Windows, install Linux and discover Go in the first place.

Knowing how to write good SQL is a superpower as a developer, and every time I've worked with an ORM fan I get this reinforced. "The database is too slow!" No, your SQL just sucks.

Most of the improvements made to any language don’t expand the community much. And they don’t have to, because that’s not the point. The point is to improve the language and ecosystem to help make better software.

Generics support is a ubiquitous feature in static programming languages. If it was included on day one in Go, nobody would have blinked an eye. This is only such a controversial topic in Go because the language maintainers made it one.

Maybe people who have only ever used ORMs are happy with them, because they don't know how much more flexible and faster "raw" SQL queries can be?

I don’t even comprehend your argument. Look: https://gorm.io/docs/, it’s full of strings everywhere. That’s as error prone as anything else and it puts an additional layer of abstraction between you and your sql.

I'm in a similar boat to sbrother (GP) and some of the other sibling commenters: like GP, I don't love the language (honestly, "patronizing" is the word that feels most accurate to describe working in Go for me, if a programming language can even be patronizing); like others, I have been impressed with how well it works when programming in its niche (high-performance network proxies).

I'd add what I think is perhaps its most significant benefit to the list: Go fully solved the function coloring I/O problem in a way few other languages (Erlang/Elixir and ... Bend? Others?) have.

That's adjacent to the concurrency benefits in the parent comment, but a little different: allowing procedural, non-colored code to be efficiently concurrent over I/O without introducing function coloring or requiring people to code specifically to an event loop/IO multiplexer in some other way requires good concurrency support in the language, to be sure. However, getting rid of function coloring while providing efficient concurrent IO also requires: a solid stdlib of IO capabilities; a very very good runtime that can coalesce goroutine-concurrent IO into multiplexing OS primitives in the same way a function-colored event loop would (while pre-empting/scheduling in a reasonable way that mitigates unexpected blocking); a strong "critical mass" of libraries to talk to common IO-ful systems; a strong community convention of "we will generally prefer reimplementing IO drivers in Go rather than binding/Cgo-ing in foreign code".

It's when you combine all of those that Go shines as a platform for concurrent (usually network) IO.

> I still remember people gaslighting everyone that any feature Go had was ESSENTIAL, and every feature Go didn't have was USELESS or too complicated for mere mortals "delivering value".

I'd say this is still the norm in discourse around Go, it's just that the goalposts have moved somewhat since it has more features now.

Go doesn't force you to either handle or propagate the error.

And the alternatives are not exceptions, of course, but ADTs.

I frequently hear that Go is simple, and I generally take that to mean that it doesn't have a whole lot of features. But doesn't this then force the complexity on the programmer? There is a set amount of complexity in the world, and either your language models it or you model it, but something has to model it for your program to be a faithful representation of the problem in question. It seems that Go has shunted much of that complexity onto the programmer. This article does a good job of summarizing (and indeed helped to shape) my thoughts on the matter: https://fasterthanli.me/articles/i-want-off-mr-golangs-wild-...

It goes like this:

1. Software development is a fashion industry.

2. OOP is currently uncool.

3. People who identify as Go programmers don’t want it to be thought of as connected to OOP at all, because then it is uncool by association.

https://github.com/stephenafamo/bob supports both CTEs and JSONB in the psql (postgres) dialect

https://bob.stephenafamo.com/docs/query-builder/psql/example...

https://github.com/stephenafamo/bob/blob/main/gen/bobgen-psq...