Go Slices

Slices in Go are similar to arrays but more dynamic and versatile. While both store multiple values of the same data type in a single variable, slices differ because their lengths can grow or shrink as needed, unlike arrays with fixed lengths.

Creating a Slice

There are three primary ways to create a slice in Go:

1. Using the []datatype{values} format
2. Creating a slice from an array
3. Using the make() function

Creating a Slice Using []datatype{values}

To declare a slice with this method:

Syntax:

sliceName := []datatype{values}

sliceName := []datatype{values}

​

For instance:

motorcycleModels := []string{}

motorcycleModels := []string{}

​

The code above creates an empty slice with both a length and capacity of 0.

To initialize a slice during its declaration:

motorcycleModels := []string{"Ducati", "Yamaha", "Honda"}

motorcycleModels := []string{"Ducati", "Yamaha", "Honda"}

​

This example declares a slice with a length and capacity of 3.

Go provides two essential functions for slice handling:

• len() returns the number of elements in the slice.
• cap() returns the capacity of the slice, i.e., the maximum number of elements it can grow to.

Example:

package main
import ("fmt")

func main() {
  emptySlice := []string{}
  fmt.Println(len(emptySlice)) // Length
  fmt.Println(cap(emptySlice)) // Capacity
  fmt.Println(emptySlice)

  initializedSlice := []string{"Suzuki", "Honda", "Yamaha", "Ducati"}
  fmt.Println(len(initializedSlice))
  fmt.Println(cap(initializedSlice))
  fmt.Println(initializedSlice)
}

package main

import ("fmt")

​

func main() {

  emptySlice := []string{}

  fmt.Println(len(emptySlice)) // Length

  fmt.Println(cap(emptySlice)) // Capacity

  fmt.Println(emptySlice)

​

  initializedSlice := []string{"Suzuki", "Honda", "Yamaha", "Ducati"}

  fmt.Println(len(initializedSlice))

  fmt.Println(cap(initializedSlice))

  fmt.Println(initializedSlice)

}

​

Output:

0
0
[]
4
4
[Suzuki Honda Yamaha Ducati]

0

0

[]

4

4

[Suzuki Honda Yamaha Ducati]

​

Here, the first slice is empty, so its length and capacity are 0. The second slice includes elements, so the length and capacity correspond to the number of those elements.

Creating a Slice from an Array

Slices can be derived from arrays by specifying a range of elements.

Syntax:

var arrayName = [length]datatype{values} // Declare an array
sliceName := arrayName[start:end] // Slice from the array

var arrayName = [length]datatype{values} // Declare an array

sliceName := arrayName[start:end] // Slice from the array

​

Example:

package main
import ("fmt")

func main() {
  motorcycleYears := [6]int{2019, 2020, 2021, 2022, 2023, 2024}
  recentYears := motorcycleYears[2:4]

  fmt.Printf("recentYears = %v\n", recentYears)
  fmt.Printf("length = %d\n", len(recentYears))
  fmt.Printf("capacity = %d\n", cap(recentYears))
}

package main

import ("fmt")

​

func main() {

  motorcycleYears := [6]int{2019, 2020, 2021, 2022, 2023, 2024}

  recentYears := motorcycleYears[2:4]

​

  fmt.Printf("recentYears = %v\n", recentYears)

  fmt.Printf("length = %d\n", len(recentYears))

  fmt.Printf("capacity = %d\n", cap(recentYears))

}

​

Output:

recentYears = [2021 2022]
length = 2
capacity = 4

recentYears = [2021 2022]

length = 2

capacity = 4

​

In this case:

• recentYears is a slice of length 2, derived from the array motorcycleYears.
• It starts from the third element (index 2) and ends before the fifth element (index 4).
• The slice’s capacity is 4 because it can grow from its starting point to the end of the array.

Creating a Slice Using the make() Function

The make() function is a powerful tool for creating slices with pre-defined lengths and capacities.

Syntax:

sliceName := make([]type, length, capacity)

sliceName := make([]type, length, capacity)

​

Note: If the capacity parameter is omitted, it defaults to the length.

Example:

package main
import ("fmt")

func main() {
  sliceWithCapacity := make([]int, 5, 10)
  fmt.Printf("sliceWithCapacity = %v\n", sliceWithCapacity)
  fmt.Printf("length = %d\n", len(sliceWithCapacity))
  fmt.Printf("capacity = %d\n", cap(sliceWithCapacity))

  sliceWithoutCapacity := make([]int, 5)
  fmt.Printf("sliceWithoutCapacity = %v\n", sliceWithoutCapacity)
  fmt.Printf("length = %d\n", len(sliceWithoutCapacity))
  fmt.Printf("capacity = %d\n", cap(sliceWithoutCapacity))
}

package main

import ("fmt")

​

func main() {

  sliceWithCapacity := make([]int, 5, 10)

  fmt.Printf("sliceWithCapacity = %v\n", sliceWithCapacity)

  fmt.Printf("length = %d\n", len(sliceWithCapacity))

  fmt.Printf("capacity = %d\n", cap(sliceWithCapacity))

​

  sliceWithoutCapacity := make([]int, 5)

  fmt.Printf("sliceWithoutCapacity = %v\n", sliceWithoutCapacity)

  fmt.Printf("length = %d\n", len(sliceWithoutCapacity))

  fmt.Printf("capacity = %d\n", cap(sliceWithoutCapacity))

}

​

Output:

sliceWithCapacity = [0 0 0 0 0]
length = 5
capacity = 10
sliceWithoutCapacity = [0 0 0 0 0]
length = 5
capacity = 5

sliceWithCapacity = [0 0 0 0 0]

length = 5

capacity = 10

sliceWithoutCapacity = [0 0 0 0 0]

length = 5

capacity = 5

​

Here:

• The first slice has a length of 5 and capacity of 10.
• The second slice’s length and capacity are both 5, as the capacity parameter is omitted.