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Comment by racingmars | Hacker News Reader

Go does have a concurrent map in the standard library, but the documentation recommends not using it unless you have specific access patterns that it's optimized for:

https://pkg.go.dev/sync#Map

You lose type safety when using it. I'm guessing with generics in 1.18 now, we'll see an updated generic version of sync.Map whenever a bunch of new collection types are added to the standard library that take advantage of generics.

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Yeah, I'm looking forward to Go's stdlib evolving useful collections now that generics exist.

Like maybe a set. That isn't a map[T]interface{} and can do things like unions and intersections so I don't have to implement it with for loops.

> That isn't a map[T]interface{}

FWIW while map[T]interface{} is somewhat more convenient to use, for efficiency reasons you should prefer map[T]struct{}: interface{} being a fat pointer is takes 16 bytes * the capacity of the map/set. struct{} is a zst, so takes 0.

It also signals much more clearly that it's a map to nothing, which is a set, a map[T]interface{} could be an actual map to a bunch of random things.

While you're not wrong, and that is how you implement a set in Go, it's still a workaround over a standard library Set type unfortunately.

But, with Go's generics, I hope they will add new collection types to the standard library.

It's actually much more common to use map[T]bool, because it allows easy membership testing just with

if m[x] { ... }

Not that I have seen. map[T]struct{} is more common, with if _,ok := m[x]; ok {} used for testing if a key is in the map. The space savings really add up with large sets.

At least at Google, map[T]bool is more common, by an order of magnitude. Probably because map[T]bool is recommended by our official style guide, which tends to favor readability over a negligible performance difference.

That is largely a distinction without a difference, the main gist of my comment was that using an interface{} value, while convenient in some ways, is way costlier than necessary (at least in memory) without any real advantage.

This is exactly why a generic Set collection should have been there since the start.

I don't disagree at all, I'm just pointing out a less than ideal pattern.

And I much appreciate your feedback :) Whenever I try to think of what was the best practice idiom, I always mix up map[T]struct{} and map[T]interface{}, due to the curly brackets at the end.

As you can tell, it's been a while since I've written Go.

Hah, 50/50 I'd get that wrong, cheers.

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