[jrockway]

A map[T]bool has 3 states for every key; absent, true, and false. A map[t]struct{} has 2 states for every key; absent, and present.

People new to Go tend to pick map[T]bool or map[T]int because they're used to using bools and ints throughout their code, but struct{} is the correct value type for sets. (That is not to say that a counting set, map[T]int is useless, however. If you need that, use that!)

[majewsky]

I usually use map[T]bool because

  if _, ok := wasTouched[thing]; !ok {
    touch(thing)
    wasTouched[thing] = struct{}{}
  }

is way uglier than

  if !wasTouched[thing] {
    touch(thing)
    wasTouched[thing] = true
  }

[masklinn]

That doesn’t actually work unless you first fill all possible values with `false`.

[fileeditview]

Wrong. The whole point of this construct is that in Go maps return default values for keys that do not exist. The default value for bool is false.