This question already has an answer here:
In the below code, why are both fmt.Println(len(people)) printing 0? As pointed out here, https://stackoverflow.com/a/2441112/315445, and elsewhere, slice is reference type. Why isn't caller (main) seeing the updated data?
package main
import "fmt"
type Person struct {
name string
age string
}
func main() {
var people = make([]Person, 0)
fmt.Println(len(people))
getList(people)
fmt.Println(len(people))
}
func getList(people []Person) {
people = append(people, Person {"Foo", "1"})
people = append(people, Person {"Bar", "2"})
}
But this works. So its not actually a pass-by-reference?
package main
import "fmt"
type Person struct {
name string
age string
}
func main() {
var people = make([]Person, 0)
fmt.Println(len(people))
people = getList(people)
fmt.Println(len(people))
}
func getList(people []Person) []Person {
people = append(people, Person {"Foo", "1"})
people = append(people, Person {"Bar", "2"})
return people
}
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A slice contains a pointer to the backing array, length and capacity. The append built-in returns a new slice with a new length and possibly a new pointer to a reallocated backing array.
Slices are passed by value. Changes to the slice in getList are not visible in the caller. Changes to the backing array are visible to the caller.
A slice is called a reference type because a slice contains a pointer to the backing array.