{"id":201,"date":"2024-09-12T15:39:58","date_gmt":"2024-09-12T08:39:58","guid":{"rendered":"https:\/\/gotutorial.org\/?page_id=201"},"modified":"2024-09-25T20:30:16","modified_gmt":"2024-09-25T13:30:16","slug":"go-slice","status":"publish","type":"page","link":"https:\/\/www.gotutorial.org\/go-tutorial\/go-slice\/","title":{"rendered":"Go Slice"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn about the Go slice and how to use it effectively.<\/p>\n\n\n\n

In Go, slices are like arrays<\/a> but have a dynamic size. By definition, a slice is a dynamically sized, flexible view into elements of an array.<\/p>\n\n\n\n

Declaring a slice<\/h2>\n\n\n\n

To declare a slice, you use the var<\/code> keyword, slice name, square brackets, and the type of the elements:<\/p>\n\n\n

var<\/span> sliceName [] type<\/span><\/code><\/span>Code language:<\/span> Go<\/span> (<\/span>go<\/span>)<\/span><\/small><\/pre>\n\n\n
var<\/span> names [] string<\/span><\/code><\/span>Code language:<\/span> Go<\/span> (<\/span>go<\/span>)<\/span><\/small><\/pre>\n\n\n
This example declares the names<\/code> slice that will store a list of strings.<\/p>\n\n\n\n
Initializing a slice<\/h2>\n\n\n\n
You can declare and initialize a slice in a single line of code like this:<\/p>\n\n\n
var<\/span> names [] string<\/span> = [] string<\/span> {\"Alice\"<\/span>, \"Bob\"<\/span>, \"John\"<\/span>}<\/code><\/span>Code language:<\/span> Go<\/span> (<\/span>go<\/span>)<\/span><\/small><\/pre>\n\n\n
Inside a function, you can use the short variable declaration to declare and initialize a slice:<\/p>\n\n\n
names := [] string<\/span> {\"Alice\"<\/span>, \"Bob\"<\/span>, \"John\"<\/span>}<\/code><\/span>Code language:<\/span> Go<\/span> (<\/span>go<\/span>)<\/span><\/small><\/pre>\n\n\n
Typically, you create a slice from an array. For example:<\/p>\n\n\n
package<\/span> main\n\nimport<\/span> \"fmt\"<\/span>\n\nfunc<\/span> main<\/span>()<\/span><\/span> {\n    guests := [3<\/span>] string<\/span>{\"Alice\"<\/span>, \"Bob\"<\/span>, \"John\"<\/span>}\n    vip := guests[0<\/span>:2<\/span>]\n\n    for<\/span> index, name := range<\/span> vip {\n        fmt.Println(index, name)\n    }\n}<\/code><\/span>Code language:<\/span> Go<\/span> (<\/span>go<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
0<\/span> Alice\n1<\/span> Bob<\/code><\/span>Code language:<\/span> Go<\/span> (<\/span>go<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, we create a slice vip<\/code> from the guests<\/code> array. The vip<\/code> slice includes the first and second elements of the guests<\/code> array. <\/p>\n\n\n\n
Modifying the slice elements<\/h2>\n\n\n\n
A slice is a reference to an underlying array. When you change an element in a slice, the corresponding element of the underlying array also changes. For example:<\/p>\n\n\n
package<\/span> main\n\nimport<\/span> \"fmt\"<\/span>\n\nfunc<\/span> main<\/span>()<\/span><\/span> {\n    guests := [3<\/span>] string<\/span> {\"Alice\"<\/span>, \"Bob\"<\/span>, \"John\"<\/span>}\n    vip := guests[0<\/span>:2<\/span>]\n    vip[0<\/span>] = \"Linda\"<\/span>\n    fmt.Println(guests)\n}<\/code><\/span>Code language:<\/span> Go<\/span> (<\/span>go<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
[Linda Bob John]<\/code><\/span>Code language:<\/span> Go<\/span> (<\/span>go<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, we change the first element of the slice vip<\/code> to Linda, the first element in the guests<\/code> array also changes.<\/p>\n\n\n\n
Length and capacity<\/h2>\n\n\n\n
Slices have two properties:<\/p>\n\n\n\n
    \n
  • Length<\/strong> stores the number of elements in the slice.<\/li>\n\n\n\n
  • Capacity<\/strong> is the number of elements in the underlying array from the index where you create the slice.<\/li>\n<\/ul>\n\n\n\n
    For example:<\/p>\n\n\n
    package<\/span> main\n\nimport<\/span> \"fmt\"<\/span>\n\nfunc<\/span> main<\/span>()<\/span><\/span> {\n    scores := []int<\/span>{1<\/span>, 2<\/span>, 3<\/span>, 4<\/span>, 5<\/span>, 6<\/span>, 7<\/span>, 8<\/span>, 9<\/span>, 10<\/span>}\n    avergeScores := scores[1<\/span>:4<\/span>]\n    fmt.Println(\"Length of slice:\"<\/span>,len<\/span>(avergeScores))\n    fmt.Println(\"Capacity of slice:\"<\/span>,cap<\/span>(avergeScores))\n}<\/code><\/span>Code language:<\/span> Go<\/span> (<\/span>go<\/span>)<\/span><\/small><\/pre>\n\n\n
    Output:<\/p>\n\n\n
    Length of slice: 3<\/span>\nCapacity of slice: 9<\/span><\/code><\/span>Code language:<\/span> Go<\/span> (<\/span>go<\/span>)<\/span><\/small><\/pre>\n\n\n
    In this example:<\/p>\n\n\n\n
      \n
    • The scores<\/code> array has 10 numbers from 1 to 10.<\/li>\n\n\n\n
    • The length of the averageScores<\/code> slice is 3 because it includes elements from the index 1 to 3 (1, 2, and 3).<\/li>\n\n\n\n
    • The capacity of the averageScores<\/code> slice is 9 because it contains elements from index 1 to the end of the array (2, 3, … 10).<\/li>\n<\/ul>\n\n\n\n
      Appending an element to a slice<\/h2>\n\n\n\n
      To append an element to a slice, you use the built-in append()<\/code> function. The append()<\/code> function adds an element at the end of the slice and returns a new slice:<\/p>\n\n\n
      package<\/span> main\n\nimport<\/span> \"fmt\"<\/span>\n\nfunc<\/span> main<\/span>()<\/span><\/span> {\n\n    names := [] string<\/span> {}\n    names = append<\/span>(names, \"Alice\"<\/span>)\n    names = append<\/span>(names, \"Bob\"<\/span>)\n    names = append<\/span>(names, \"Joe\"<\/span>)\n\n    for<\/span> index, name := range<\/span> names {\n        fmt.Println(index, name)\n    }\n}<\/code><\/span>Code language:<\/span> Go<\/span> (<\/span>go<\/span>)<\/span><\/small><\/pre>\n\n\n
      Output:<\/p>\n\n\n
      0<\/span> Alice\n1<\/span> Bob\n2<\/span> Joe<\/code><\/span>Code language:<\/span> Go<\/span> (<\/span>go<\/span>)<\/span><\/small><\/pre>\n\n\n
      Summary<\/h2>\n\n\n\n
        \n
      • A slice is a view into an underlying array and provides a more flexible interface.<\/li>\n\n\n\n
      • Use the array[start:end]<\/code> syntax to create a slice from an array.<\/li>\n\n\n\n
      • Use the len<\/code> function to get the number of elements in a slice.<\/li>\n\n\n\n
      • Use the cap<\/code> function to get the capacity of a slice.<\/li>\n<\/ul>\n
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The for range<\/a> iterates over elements of the vip<\/code> slice and displays their indexes and values on the screen.<\/p>\n\n\n\n
This syntax is similar to declaring an array<\/a> except that it does not have a fixed size. Therefore, we don’t have to specify the size in the square brackets. For example:<\/p>\n\n\n