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slice-nil.md

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nil is a valid slice

nil is a valid slice of length 0. This means that,

  • You should not return a slice of length zero explicitly. Return nil instead.

    BadGood
     
    if x == "" {
  return []int{}
}
    		 
    if x == "" {
  return nil
}

  • To check if a slice is empty, always use len(s) == 0. Do not check for nil.

    BadGood
     
    func isEmpty(s []string) bool {
  return s == nil
}
    		 
    func isEmpty(s []string) bool {
  return len(s) == 0
}

  • The zero value (a slice declared with var) is usable immediately without make().

    BadGood
     
    nums := []int{}
// or, nums := make([]int)

if add1 {
  nums = append(nums, 1)
}

if add2 {
  nums = append(nums, 2)
}
    		 
    var nums []int

if add1 {
  nums = append(nums, 1)
}

if add2 {
  nums = append(nums, 2)
}

Remember that, while it is a valid slice, a nil slice is not equivalent to an allocated slice of length 0 - one is nil and the other is not - and the two may be treated differently in different situations (such as serialization).