Compute the size of a map in Golang.

hashmap.go

// We're going to compute the actual size of the map, it's total memory footprint.
// In retrospect, we only need the keySize, but I like it, so I'll leave it.
func computeSize(theMap map[string]interface{}) (int, int, int) {
	mapLen := uintptr(len(theMap))
	baseSize := unsafe.Sizeof(hmapRef{}) + (mapLen * 8)
	keySize := mapLen * 8 * unsafe.Sizeof(randKey(theMap))
	valSize := mapLen * 8 * unsafe.Sizeof(theMap[randKey(theMap)])
	totalSize := baseSize + keySize + valSize
	return int(keySize), int(valSize), int(totalSize)
}

func randKey(items map[string]interface{}) string {
	for k := range items {
		return k
	}
	return ""
}

//go:linkname hmapRef runtime.hmap
type hmapRef struct{}