5 ms·

There is a slight difference between the two. With a map[†]bool, you can do something like: if myset[thing] { ... } With a map[T]struct(), you end up with: i

There is a slight difference between the two. With a map[†]bool, you can do something like: if myset[thing] { ... } With a map[T]struct(), you end up with: if _, ok := myset[thing]; ok { ... } Sometimes, the saving in space is TOTALLY worth the extra verbosity. Sometimes, the slight clarity from "non-existent keys return the zero value" wins.

morelisp 5y ago
Well, now there's no excuse for not having `myset.Contains(thing)` (though there really wasn't before either) which is even clearer.
thegeekpirate 5y ago
You've also opened yourself up to bugs by allowing the map values to be "false". Using a "set's" value in an if statement doesn't make sense either, compared to if _, exists := something[item]; exists { ... } which is explicit regarding what's actually going on. As Rob said, "Clear is better than clever." https://www.youtube.com/watch?v=PAAkCSZUG1c&t=875s https://www.youtube.com/watch?v=PAAkCSZUG1c&t=875s I also don't want to be hunting down whoever creates a map[T]bool and doesn't leave a comment explaining it's a set ;) Hopefully we won't have to worry about it for much longer regardless, since I imagine we'll be using proper sets (with methods) some point in the near future.
- randomswede 5y ago
  I would say that "exists in the set" is determined only and exactly by "mySet[thing]" returning true, not that there happens to be a key in the map. But, that's one of those "requires extensive documentation" (and ideally, wrapping in a custom type and provide methods for checking and manipulating the set(s)).
  - yencabulator 5y ago
    Now every range over your set is likely to be a bug. `map[T]bool` is simply a bad design to use.
    - randomswede 5y ago
      How? Why? If you use the map[T]bool, you obviously need to pay attention to the bool value, even in a range. Whereas in map[T]struct{} you don't need to pay attention to the values. In either way, even with that type of data type underlying a set, I would (probably) provide a functional API to interact with it.
      - yencabulator 5y ago
        m["x"] = foo() for k := range { // if foo returned false, this is buggy }
        randomswede 5y ago
        Yes, as I said, if you use a map[T]bool, you need to use something like: for k, v := range m { if v { } } But it also allows you to use "if m[key] { ... }". It is literally a trade-off for what convenience you want. And in both cases, you should (probably) wrap an abstraction around the raw map.

morelisp 5y ago

Well, now there's no excuse for not having `myset.Contains(thing)` (though there really wasn't before either) which is even clearer.

thegeekpirate 5y ago

You've also opened yourself up to bugs by allowing the map values to be "false". Using a "set's" value in an if statement doesn't make sense either, compared to if _, exists := something[item]; exists { ... } which is explicit regarding what's actually going on. As Rob said, "Clear is better than clever." https://www.youtube.com/watch?v=PAAkCSZUG1c&t=875s https://www.youtube.com/watch?v=PAAkCSZUG1c&t=875s I also don't want to be hunting down whoever creates a map[T]bool and doesn't leave a comment explaining it's a set ;) Hopefully we won't have to worry about it for much longer regardless, since I imagine we'll be using proper sets (with methods) some point in the near future.

randomswede 5y ago
I would say that "exists in the set" is determined only and exactly by "mySet[thing]" returning true, not that there happens to be a key in the map. But, that's one of those "requires extensive documentation" (and ideally, wrapping in a custom type and provide methods for checking and manipulating the set(s)).
- yencabulator 5y ago
  Now every range over your set is likely to be a bug. `map[T]bool` is simply a bad design to use.
  - randomswede 5y ago
    How? Why? If you use the map[T]bool, you obviously need to pay attention to the bool value, even in a range. Whereas in map[T]struct{} you don't need to pay attention to the values. In either way, even with that type of data type underlying a set, I would (probably) provide a functional API to interact with it.
    - yencabulator 5y ago
      m["x"] = foo() for k := range { // if foo returned false, this is buggy }
      - randomswede 5y ago
        Yes, as I said, if you use a map[T]bool, you need to use something like: for k, v := range m { if v { } } But it also allows you to use "if m[key] { ... }". It is literally a trade-off for what convenience you want. And in both cases, you should (probably) wrap an abstraction around the raw map.