Generic Methods in Go 1.27

Generic Methods in Go 1.27(dominik.info)

71 points by EspressoGPT 45 days ago | 47 comments

throwaw12 45 days ago |

people working actively in "modern" Go codebases with generics, is it becoming like a Java/Spring kind of codebase?

I understand why you might need generics, but I hate how Java ecosystem exploits it so much that, reading code becomes so difficult, because it was inherited from 10 levels of parent classes and in some cases Java Beans get created based on generic types and their parent classes are abstract classes.

throw-the-towel 45 days ago | |

I remember my coworkers having managed to write Java in pre-generics Go. The code had functions wrapped in functions wrapped in yet more functions, and interfaces only ever implemented by one type to replace the generics abuse. Life finds a way.

zimpenfish 45 days ago | | |

Yeah, Go people were always been perfectly capable of creating abominational messes before generics arrived. Once you've looked at an interface referencing an interface referencing an interface referencing an interface which is only ever instantiated by one (1) type, you realise that all hope has been lost and your only recourse is blatant sarcasm, pointed replies on Slack[0] and PRs, and finding the perpetrators after dark with a big sack of flour.

[0] Other corporate messaging systems are available.

bbkane 45 days ago | | |

Entropy finds a way :)

pjmlp 45 days ago | |

People like to blame Java for enterprise code, except they forget enterprise has been writing enterprisy code since Fortran, COBOL and Lisp days.

I have found Spring like magic with pre-processor macros, sed and awk, in the glory days of Yourdon Structured Method and enterprisy C code.

masklinn 45 days ago | | |

Having had the displeasure of working with struts, enterprise definitely never needed generics to enterprise.

jerf 45 days ago | |

"people working actively in "modern" Go codebases with generics, is it becoming like a Java/Spring kind of codebase?"

I have yet to encounter a 3rd party library that uses generics that isn't a data structure library of some sort. The only person I have seen doing crazy things with generics is... me. In my own code, for the most part [1]. In general I don't even see generics that are so much as parameterized by a meaningful interface like "type BlahBlah[R io.Reader]"; generics are so often parameterized by "any" that a casual reader might be forgiven for thinking that that is all a Go generic can do. As is often the case, the most complicated generic type signatures are the one in the standard library and even they aren't really all that bad, it's really just about the "~" operator allowing support for "all types that are either 'string' or something of the form 'type X string'".

I see the occasional person complain about how generics have ruined Go by making them too complicated. I push back on them with basically the previous paragraph. None of them have ever replied to press their point any farther. I interpret this to mean that their experience with the feature is in fact the same. At this point if you're buried in super complicated generics it is almost certainly someone on your own team and you should tell them to stop.

Similarly for iterators, by the way. The way Go did iterators is a bit odd to implement them yourself. Won't deny that. But it does compile down very efficiently, and only matters to the people writing the iterator not the consumer. Anyone who claims it has wrecked the language is invited to explain to me why it is that they are writing so many dozens of iterators all the time first, because as near as I can tell they aren't getting that from 3rd party libraries or the standard library.

[1]: The exception being https://github.com/thejerf/mtmap if you want to see something that I did find a use for, and you may have a use for, but is not something I would suggest using all the time. Very specific use case I had.

zbentley 45 days ago | | |

I’ve found generics useful at handling database-backed objects at the write boundary. Since the layout of those objects is generally pretty important, having middleware-ish things that handle interface/supertypes but return generic concrete types saves on a lot of reflection and casting.

mrkeen 45 days ago | |

Neither Go nor Java's generics is rich enough for the problems you describe. They give you the means to turn IntList into List<I>, but not into <L>Int or <L><I>.

So I doubt the famous AbstractProxyBeanInterceptors are coming from an overuse of generics.

pjmlp 44 days ago | | |

The irony is that while people bash on Java, Objective-C manages to have even longer names.

riobard 45 days ago | |

> inherited from 10 levels of parent classes

This is not (yet) a thing in Go. Go does not have classes and inheritance. Interface is more like duck-typing.

Zanfa 45 days ago | | |

But you can do equally horrible inheritance-y things with embedded structs.

eberkund 45 days ago | |

I think Go is more commonly used in modern microservice architectures rather than in older monolithic architectures where the kind of Java code you're describing happens. Might have some impact on the level of complexity that can get out of hand.

In the Go codebases I have worked on, generics were not overused IMHO. It did allow us to get rid of some type specific helper functions and made collection based operations like sorting a lot nicer to work with.

saturn_vk 45 days ago | |

I’ve written generic code once or twice per year. Usage through libraries is higher, though it’s not very visible.

dwaite 44 days ago | |

Java has its own problems with generics, such as the near-lack of runtime representation or the lack of a This/Self type, as well as limited variance, leading to signatures like `public abstract class Enum<E extends Enum<E>>`.

IMHO these all go back to design compromises due to the desire to make generics optional - but now, over two decades later, are Java generics really optional?

The ten levels of parent classes is its own issue with Java - with interfaces and class inheritance being a good half of your mechanisms for abstractions in the code base, with adapters making up the other half.

nicoburns 45 days ago | |

Rust has had generics for 10 years and doesn't have this problem. I think it's more a culture problem in Java than anything (and arguably a historical one).

cryptos 44 days ago | | |

And in the end it might be a culture problem in the contexts Java is used in.

ad_hockey 45 days ago | |

I haven't seen that in the large codebase at work, for what it's worth. The thing that's surprised me about generics in Go is how rarely they're needed in practice. Very nice to have in the right place, but the vast majority of our source files still get along fine with plain old typed maps and slices.

vrosas 45 days ago | |

I have been a full-time go developer since 2015 and I have quite literally never written a line of generic go code. I can't even recall seeing any written at any {job} since they've been introduced...

tancop 45 days ago |

> Go’s interface system works at runtime. The specific type of a value passed into an interface parameter is resolved while the program runs. This dynamic dispatch clashes with generics being resolved at compile time.

What if the compiler generated both vtable and monomorphized variants for each method? Most calls would use the static version but places that need it like interface generics call the virtual method.

masklinn 45 days ago | |

The problem is that your vtable would have to have a monomorphised copy of the generic method for each possible instance, this requires whole program analysis just to generate the interface — and even then I would not be surprised if you could generate calls which the compiler was not able to relate to the interface — and then you get to the potential size explosion of your vtable as it has to hold an unbounded number of methods.

Note that despite having much stronger static semantics and much weaker reflection than Go Rust has the exact same limitation: a trait method with a non-lifetime generic parameter is not dyn-compatible. C++ is the same, a template member function (generic method) can’t be virtual (dynamically dispatched).

saturn_vk 45 days ago | |

vtables still need types, and a generic method that is not yet instantiated will not have them

dekdrop 45 days ago |

TIL

> However, Go’s interface system works at runtime. The specific type of a value passed into an interface parameter is resolved while the program runs.

mknyszek 45 days ago | |

There's a little more nuance to this. The compiler knows the static type of any value placed into an interface value, and emits code to place a concrete type pointer (or itab pointer) into the interface value. You can see this in the disassembly.

Later when you pass this value around and assign it to places, sure, there may be a different type depending on where the interface value came from. But the construction of these values is very much static.

In this sense I wouldn't really call this "resolv[ing] while the program runs" unless you take a very broad sense of "resolution."

masklinn 45 days ago | | |

The construction of interface values is a very shallow mean and essentially irrelevant to the need for interfaces.

Whereas the runtime resolution of operations performed through an interface (dynamic dispatch) is the primary purpose of and use care for interfaces, with the dynamic resolution of wrapped types (type erasure / downcasts / type switches) is the secondary one.

DrCiphers 45 days ago |

So Go is becoming Java?

saturn_vk 45 days ago | |

Absolutely. If you’ve never used Java or Go

bmurphy1976 45 days ago | |

Maybe. It's been what I wished Java was since the beginning, personally.

EdSchouten 45 days ago |

Go is often thought of as a successor of C. C doesn't have methods, only global functions. From my perspective, Go added methods primarily so that you can use them in combination with interfaces. Given that interfaces don't support generic methods, I'm personally not convinced that this feature was worth adding.

munificent 45 days ago | |

> From my perspective, Go added methods primarily so that you can use them in combination with interfaces.

They also give you a limited form of overloading. Without methods or overloading, you end up in the situation that C and Scheme are in where every operation on a data structure has to redundantly have the data structure in its name like:

    list_clear(my_list);
    queue_clear(my_queue);
    map_clear(my_map);

kune 45 days ago | | |

In Go you would methods for that: my_list.Clear(), my_queue.Clear() and my_map.Clear(). Now you can define a Clearer interface, which has only the Clear method. That allows you to write a function clearAndLog(item Clearer) and it will work with the list, queue and map.

so-cal-schemer 45 days ago | | |

I just want to leave this here:

SICP: 2.5 Systems with Generic Operations

https://sarabander.github.io/sicp/html/2_002e5.xhtml

wasmperson 45 days ago | | |

> Without methods or overloading, you end up in the situation that C and Scheme are in

Well in C at least we now have this:

  #define clear(s) _Generic((s) \
          ,struct list: list_clear \
          ,struct queue: queue_clear \
          ,struct map: map_clear \
  )(s)

  clear(my_map);
  clear(my_list);
  clear(my_queue);

...although it turns out the other nice thing about methods is automatic namespacing.

pjmlp 45 days ago | |

Well, C has a kind of pseudo generics since C11.

And everyone gets to invent their own vtable implementation since the 1980's.

etse 45 days ago | |

What was the reason for interfaces having to work at runtime?

#define clear(s) _Generic((s) \ ,struct list: list_clear \ ,struct queue: queue_clear \ ,struct map: map_clear \ )(s) clear(my_map); clear(my_list); clear(my_queue);