Prepend

Go has a built-in append function which add elements in the slice: 

  1. func append(slice []Type, elems ...Type) []Type

But how if we want to the “prepend” effect? Maybe we should use copy function. E.g.: 

  1. package main
  3. import "fmt"
  5. func main()  {
  6.     var s []int = []int{1, 2}
  7.     fmt.Println(s)
  9.     s1 := make([]int, len(s) + 1)
  10.     s1[0] = 0
  11.     copy(s1[1:], s)
  12.     s = s1
  13.     fmt.Println(s)
  15. }

The result is like this: 

  1. [1 2]
  2. [0 1 2]

But the above code looks ugly and cumbersome, so an elegant implementation maybe here: 

  1. s = append([]int{0}, s...)

BTW, I also have tried to write a “general-purpose” prepend: 

  1. func Prepend(v interface{}, slice []interface{}) []interface{}{
  2.     return append([]interface{}{v}, slice...)
  3. }

But since []T can’t convert to an []interface{} directly (please refer https://golang.org/doc/faq#convert_slice_of_interface, it is just a toy, not useful.

Reference:
Go – append/prepend item into slice.