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Slices

A Slice is like a dynamically-sized array. A slice type is written []T,where elements has type T. So it’s like an array without size defined.

A Slice is a light weight data structure that gives access to sequence of elements of an array, also known as slice’s underlying array.

Syntax

a[i:j]– Slice with range from i to j
a[i:]– Slice with range from i to end of the underlying array
a[:j]– Slice with range from start of the underlying array to j
a[:]– Slice, whose range is the whole array

Example

Consider the example below, arr is an array of size 5 and arr[1:4]slices it from index 1 to 3So it excludes the last one.

package main

import "fmt"

func main() {
  arr := [4]int{1, 2, 3, 4} 
  var s1 []int = arr[0:2]
  var s2 []int = arr[1:3]
  fmt.Println(s1)
  fmt.Println(s2)
}

Result

[1 2]
[2 3]

If we represent this in a mathematical fashion, slice operator is s[i:j] where 0<=i<=j<=cap(s)

Length and Capacity

Length: Length is the number of slice elements
Capacity: Capacity is the number of elements between start of slice and the end of underlying array.

The Length and capacity of a slice is defined by the function len() and cap()For the Same example above, let’s execute below,

package main
import "fmt"
func main(){
  arr := [6]int {1,2,3,4,5,6}
  var s1 []int  = arr[3:4]

  fmt.Println(s1)
  fmt.Println(len(s1),cap(s1))
}

Result

[4]
1 3

Note: A slice does not store any data, it only describes a section of an underlying array. Changing the elements of a slice will modify the corresponding elements of its underlying array

Consider the below declaration, by no defining the size of the array, the compiler will recognize this as a slice and will create the underlying array first and then creates slice pointing it

sli := []int{1,2,3}