Golang questions

• package main
   
  import "fmt"
   
  func main() {
  	a := []int{1, 2, 3}
  	a = a[:0]
  	fmt.Println(a, len(a), cap(a))
  } // [] 0 3

• package main
   
  import "fmt"
   
  func main() {
  	a := []int{1, 2, 3}
  	a = nil
  	fmt.Println(a, len(a), cap(a))
  } // [] 0 0