4 ms·

Sincere question out of curiosity, since I have not been exposed to Go at all. How do container types, like arrays or hashmaps work without generics? Do you ba

• jimsmart 5y ago
  Arrays/slices and maps are in fact provided as built-ins that function like generics, e.g. []foo and map[foo]bar work as expected, as do associated helper methods. But those are the only container types with built-in support like that. (Channels can similarly be of any type)
• zeugmasyllepsis 5y ago
  Go supports a handful of built-in generic types, like hashmaps. What Go currently lacks is user-defined generics, though that is actively being worked on.
• tptacek 5y ago
  Roughly the same way containers work in Python.
  • dragonwriter 5y ago
    > Roughly the same way containers work in Python. That’s not really true, since built-in containers are special sui generis generics in Go, whereas in an untyped python they get by being untyped, and in python’s statically-checked type system (as implemented in pyright, mypy, etc.) they use general-purpose generics.
    • tptacek 5y ago
      That complaint is as old as the language --- the first piece about Go I ever read, after my friend Yan convinced me to pick up Go, called it out for having "generics for me and no generics for thee". I've never understood why I'm meant to care. I get, if you want to write your own generic containers, being irritated that there aren't universally available generics (yet). I don't get being upset that the language has some special-cased generics. It's not personal. They're not rubbing salt in your wounds. They just need a map type that works. At any rate: the person asking the question is wondering how you manage to have performant containers with reasonable interfaces in a language without generics. That's a good question! If you've worked a lot in C, you might be imagining a horrible mess of void-stars or something. But no, the ergonomics are basically those of Python, with extra typing.
      • dragonwriter 5y ago
        > That complaint is as old as the language I’m not making a complaint, I’m pointing out a fact without a value judgement. > At any rate: the person asking the question is wondering how you manage to have performant containers with reasonable interfaces in a language without generics. Uh, I don’t see either “performant” or “with reasonable interfaces” there, the question is: “How do container types, like arrays or hashmaps work without generics? Do you basically have to declare and implement types/methods for each different contained type?” The answer is, for built-in containers, “no, because they use special-purpose generics”. For custom containers, its basically “yes”, but you probably only want a single contained type with an appropriate interface anyway. In neither case is “basically the same as Python” particularly accurate, though I suppose the former case is similar to typed python using generics in the same way as any language with generics would be, while the latter is loosely similar to bare Python or typed Python using protocols instead of generics. But only loosely.
        • tptacek 5y ago
          Yeah, I'm choosing not to die on this hill. I'm just saying that Go has first-class table and resizable array ADTs.
          • masklinn 5y ago
            They’re not first class though: you can not take in, return, or work with the ADTs, only with concrete instances of them.
            • tptacek 5y ago
              Hey, there, I'm over on this other hill now, not dying on that one. :)
        • masklinn 5y ago
          > The answer is, for built-in containers, “no, because they use special-purpose generics”. Unless you want to implement utility helpers working on them then it’s yes again, because Go doesn’t have generic functions either, so while it does have a few builtin generic containers, you can’t operate genetically over them.
• void_mint 5y ago
  Others have answered, but I just wanted to add, your question is usually where beginners/non Go users start to pearl-clutch. I would advise, if you're curious, to give it a shot for a while. As with all new things, try to not just write the language you're used to, but in the syntax of the language you're using, and instead embrace patterns that exist in a given language. Lots of people find the things you're concerned about missing to not really be the end of the world. Or you might hate it, and that's also okay.
• SiVal 5y ago
  I hardly ever need generics directly. If I have to write an algorithm for 2 types, I can copy and tweak as easily as I can deal with the added complexity of programming with abstract types. BUT, I need generics all the time indirectly. I've worked in lots of languages over the decades, and I highly value languages with mature/debugged/optimized standard libraries of algorithms and data types (esp. "containers"). Go has an impoverished subset "built-in", and that's all it offers. One of the best things about Go is the high quality of its standard libraries--where it has standard libraries--so there is a gaping hole where the container and algo libraries ought to be. Experts in these algorithms could take advantage of Go's concurrency for example to write library algorithms that provide a combination of performance and safety that I couldn't create quickly if at all. They could, that is, if they had generics in the language, but they don't, so I'm on my own (for now). When people (repeatedly) claim that Go doesn't really need generics because they (the claimants) hardly ever need generics, I have to wonder whether their knowledge of DS and algos is especially high or especially low: that they could whip up a debugged and optimized algo as easily as calling it from a library or whether they aren't even aware of the DS/algo that they really ought to be using.
  • catlifeonmars 5y ago
    Personally, it’s very rare that I need to reach for a specialized algorithm. I’m not sure if that’s primarily the problem space I work in (services providing user identity and access management), but I never find the need to go beyond a brute force search or need a data structure other than an array or built in hash map (sometimes a concurrent hash map). Most of the optimization I do involves eliminating network calls and implementing caching.
• takeda 5y ago
  They use hack of "interface{}" which does type checking at runtime (slow). And you then cast it to a proper type. If I remember correctly (haven't used it in a year) Go cheats a bit, and it has few functions in standard library that do have generics (like make), it just doesn't provide this functionality to the developer.
  • loopz 5y ago
    If you can avoid interface{} you should, ie. by declaring interfaces to types and using them explicitly. You can then mix your own types, and still be protected by the type system.
    • takeda 5y ago
      Yes, but that requires generics and without them code generators (and if you don't use them, a lot of copy & paste).