I am using this construct to simulate a set
type MyType uint8
map[MyType]interface{}
I then add in all my keys and map them to nil.
I've learnt that it is also possible to use
map[MyType]struct{}
Any benefits of using the empty struct versus interface{}.
Memory usage. For example, types struct{}, interface{}, and bool,
package main
import (
"fmt"
"unsafe"
)
func main() {
var s struct{}
fmt.Println(unsafe.Sizeof(s))
var i interface{}
fmt.Println(unsafe.Sizeof(i))
var b bool
fmt.Println(unsafe.Sizeof(b))
}
Output (bytes for 32-bit architecture):
0
8
1
Output (bytes for 64-bit architecture):
0
16
1
References:
struct{} element value occupies zero bytes.map[struct{}]struct{}? It would have a zero sized key and a zero sized value but you could put 1 thing it (also zero sized).bool instead of type map.The empty struct and empty interface, though syntactically similar, are actually opposites. An empty struct holds no data; an empty interface can hold any type of value. If I see a map[MyType]struct{}, I know immediately that no values will be stored, only keys. If I see a map[MyType]interface{}, my first impression will be that it is a heterogenous collection of values. Even if I see code storing nil in it, I won't know for sure that some other piece of code doesn't store something else in it.
In other words, using struct{} makes your code much more readable. It also saves a little memory, as described in the other answer, but that is just a fringe benefit of using the right tool for the job.
map[MyType]bool?
map[MyType]bool myself, because it can be used directly in an if condition, and it would probably produce the most readable code. But the OP only asked about struct and interface, and I wanted to keep my answer simple. (And map[MyType]struct{} is a recognized idiom for sets.)I would like to add additional detail about empty struct , as differences are already covered by andybalholm and peterSO .
Below is the example which shows usability of empty struct .
Creates an instance of rectangle struct by using a pointer address operator is denoted by & symbol.
package main
import "fmt"
type rectangle struct {
length int
breadth int
color string
}
func main() {
var rect1 = &rectangle{10, 20, "Green"} // Can't skip any value
fmt.Println(rect1)
var rect2 = &rectangle{}
rect2.length = 10
rect2.color = "Red"
fmt.Println(rect2) // breadth skipped
var rect3 = &rectangle{}
(*rect3).breadth = 10
(*rect3).color = "Blue"
fmt.Println(rect3) // length skipped
}
Reference : https://www.golangprograms.com/go-language/struct.html
For a thorough read you can refer : https://dave.cheney.net/2014/03/25/the-empty-struct
