Slice Internals

Fill in the blank in line A, to assure that printOriginalSlice will print the original slice of a subslice 

  1. package main
  3. import (
  4.     "fmt"
  5.     "reflect"
  6.     "unsafe"
  7. )
  9. const M = 10
  10. const N = 5
  12. func printOriginalSlice(subslice *[]int) {
  13.     data := __ //A
  15.     fmt.Printf("original\t%p:%+v\n", data, *data)
  16. }
  18. func main() {
  19.     slice := make([]int, M)
  20.     for i, _ := range slice {
  21.         slice[i] = i
  22.     }
  23.     subslice := slice[0:N]
  25.     fmt.Printf("slice\t%p:%+v\n", &slice, slice)
  26.     fmt.Printf("subslice\t%p:%+v\n", &subslice, subslice)
  27.     printOriginalSlice(&subslice)
  28. }

Answer

  2. package main
  4. import (
  5.     "fmt"
  6.     "reflect"
  7.     "unsafe"
  8. )
  10. const M = 10
  11. const N = 5
  13. func printOriginalSlice(subslice *[]int) {
  14.     data := (*[M]int)(unsafe.Pointer(((*reflect.SliceHeader)(unsafe.Pointer(subslice))).Data))
  16.     fmt.Printf("original\t%p:%+v\n", data, *data)
  17. }
  19. func main() {
  20.     slice := make([]int, M)
  21.     for i, _ := range slice {
  22.         slice[i] = i
  23.     }
  24.     subslice := slice[0:N]
  26.     fmt.Printf("slice\t%p:%+v\n", &slice, slice)
  27.     fmt.Printf("subslice\t%p:%+v\n", &subslice, subslice)
  28.     printOriginalSlice(&subslice)
  29. }
  31.