Compare allocation size for different type of map values for "set" type containers, where only the keys are of any interest.

mapbench_test.go

package main_test

import "testing"

func BenchmarkBoolMap(b *testing.B) {
	m := map[int]bool{}
	for i := 0; i < b.N; i++ {
		m[i] = true
	}
}

func BenchmarkEmptyStructMap(b *testing.B) {
	m := map[int]struct{}{}
	for i := 0; i < b.N; i++ {
		m[i] = struct{}{}
	}
}

func BenchmarkEmptyInterfaceMap(b *testing.B) {
	m := map[int]interface{}{}
	for i := 0; i < b.N; i++ {
		m[i] = nil
	}
}

Empty struct is the winner:

$ go test -v -bench=. -benchmem .
goos: linux
goarch: amd64
cpu: Intel(R) Core(TM) i5-8250U CPU @ 1.60GHz
BenchmarkBoolMap
BenchmarkBoolMap-8               4379631               296.6 ns/op            50 B/op          0 allocs/op
BenchmarkEmptyStructMap
BenchmarkEmptyStructMap-8        5033970               256.1 ns/op            39 B/op          0 allocs/op
BenchmarkEmptyInterfaceMap
BenchmarkEmptyInterfaceMap-8     3737322               376.0 ns/op           132 B/op          0 allocs/op
PASS
ok      _/home/cpro/work/experiments/mapbench   5.852s