package main
import "fmt"
func main() {
a := []int{1, 2, 3, 4, 5}
b := append(a[:3], 6, 7)
fmt.Println("a is ", a)
fmt.Println("b is ", b)
}
The above program prints
a is [1, 2, 3, 6, 7]
b is [1, 2, 3, 6, 7]
I understand the output of b. But why did slice a change?
Shouldn't a[:3] create a new anonymous slice and append 6,7 and return that to b instead of changing the original(a) slice? Why did append act on the original slice?
NOTICE append function will create new slide if your slice is not sufficient (overflow). See difference between two examples:
func main() {
a := []int{1, 2, 3, 4, 5}
b := append(a[:3], 6, 7) // add 2 elements, not overflow slice, doesnt create new slice
fmt.Println("a is ", a)
fmt.Println("b is ", b)
}
result
a is [1, 2, 3, 6, 7]
b is [1, 2, 3, 6, 7]
And
func main() {
a := []int{1, 2, 3, 4, 5}
b := append(a[:3], 6, 7, 8) // add 3 elements, overflow slice, create new slice
fmt.Println("a is ", a)
fmt.Println("b is ", b)
}
Result
a is [1 2 3 4 5]
b is [1 2 3 6 7 8]
I slightly modified your program to make it more clear
package main
import "fmt"
func main() {
a := []int{1, 2, 3, 4, 5}
b := a[:3] // Here Slicing does not copy the slice's data. It creates a new slice value that points to the original array
b = append(b, 6, 7)
fmt.Println("a is ", a)
fmt.Println("b is ", b)
}
Refer this Document for more reading !!
