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This looks like plain old enum in plain c. Did I miss something that makes it remarkable?

• akira2501 2y ago
  > This looks like plain old enum in plain c. It very nearly is. > Did I miss something that makes it remarkable? Yes. The literal 'iota' keyword. There is no equivalent to this in C.
  • Brian_K_White 2y ago
    How is that remarkable? Does it have some other actual function and this article is only saying how btw it can also be used to make ersatz enums?
    • akira2501 2y ago
      > make ersatz enums? The author is describing 'iota'. You can easily combine this technique with a custom type wrapper which provides the "full enum" if that's actually what you need. In which case this provides a level of capability and convenience above that of C. In practice, it really is quite remarkable, when you first use it to it's fullest extent.
  • plorkyeran 2y ago
    The basic use of iota is just what C enums do by default.
    • akira2501 2y ago
      That's one of potentially unlimited use cases. iota composes with just about any static math expression to generate almost any kind of sequence. The most common is obviously conveniently constructing bit vectors; which is possible in C, but not as an automatically composed sequence. This really is a nice feature in practice and certainly not the only type of convenient sequence you can create. A contrived example might be: const ( A rune = 'A' + iota B ) func main() { fmt.Printf("Hello %c", B) } You can, of course, just write it like a C enum if you were so inclined and that willing to go out of your way to show your disinterest in something.
      • kelnos 2y ago
        > You can, of course, just write it like a C enum if you were so inclined and that willing to go out of your way to show your disinterest in something. Oh c'mon, that's a cheap shot. Your example is odd, as it doesn't really show off anything interesting; I can indeed write it as a C enum, and I can do it with less typing: enum { A = 'A', B, }; iota doesn't really do anything interesting there. Much more interesting, IMO, was the example in the article where it can be used to easily construct bitfields. That shows off the "just about any static math expression" that you point out. I think my problem with it overall is that it's weird and unexpected. Even when it can be genuinely useful, it doesn't really fit in the language as a part of syntax. Then again, I feel like that's pretty common for Go.
        • unsnap_biceps 2y ago
          Does B == 'B' in your example?
          • plorkyeran 2y ago
            Yes, C enums increment by one for each case if no value is specified.
• iterance 2y ago
  The answer is supposed to be "iota itself is unusual," but imo iota is not really remarkable by itself. I mean it's nice, it's not pointless (though arguably it isn't parsimonious), but you could just type in the numbers. It's not saving you that much. What I'd really want is something that clearly differentiates enums where the values do matter and the values don't matter, which iota comes so close to being, but then you can do math with it. To use their example, it doesn't really matter if "electron" is 4 or 8 or whatever, but I'm sure as hell not going to assign 5 to January.
• Someone 2y ago
  The thing that’s remarkable is that, with iota, you can specify an expression that computes the enum value: For example, this: const ( Foo = 2 * iota // 0 Bar = 2 * iota // 2 Baz = 3 * iota // 6 // ... ) It typically is combined with another feature, explicit repetition of the last non-empty expression list (https://go.dev/ref/spec#Constant_declarations https://go.dev/ref/spec#Constant_declarations) to avoid having to repeat the iota expression. For a powerful example see https://go.dev/ref/spec#Iota https://go.dev/ref/spec#Iota: By definition, multiple uses of iota in the same ConstSpec all have the same value: const ( bit0, mask0 = 1 << iota, 1<<iota - 1 // bit0 == 1, mask0 == 0 (iota == 0) bit1, mask1 // bit1 == 2, mask1 == 1 (iota == 1) _, _ // (iota == 2, unused) bit3, mask3 // bit3 == 8, mask3 == 7 (iota == 3) ) I think that’s bordering on “too smart for it’s own good”, but it does prevent a very common copy-paste bug in C, where one would write something like enum { bit0 = 1 << 0, bit1 = 1 << 1, bit3 = 1 << 3, mask0 = bit0 - 1 mask1 = bit1 - 1, mask3 = bit1 - 1 // copy-paste error } (Happens fairly easily in real world code when the Enums are long, and extra Enums get added over time)
  • Brian_K_White 2y ago
    Thank you. Arbitrary expression is what I was missing.
• pjmlp 2y ago
  It is Go, apparently having plain old enums is too advanced.
  • sir_eliah 2y ago
    It's one of my major pain points with Go. When can we have proper enum support with compile-time checks whether all the enum values are exhausted?
    • kubb 2y ago
      In about 10 years, maybe :)